The Grand Canyon State hasn't voted for a Democratic presidential candidate since Bill Clinton in 1996, but Democrats believe that increased Hispanic voter registration will keep things competitive.
Recent polling has given Republican Donald Trump a slight edge over Democrat Hillary Clinton, but Democrats cite an advantage in early voting as evidence that it could be a close night. On Friday, the final day of early voting, thousands of Arizonans stood in long lines.
Two other races in the state also signal the growing power of the state's Latino voters.
Sen. John McCain (R-Ariz.), the 2008 Republican presidential nominee who has tepidly stood by Trump's candidacy this year, is running for a sixth term. McCain appears headed to victory due partly to modest Latino support.
Maricopa County Sheriff Joe Arpaio, a Republican who became a polarizing national figure in the debate over immigration and border control, is facing the toughest reelection of his 24-year reign amid tussles with the Justice Department. National liberal and Hispanic groups have targeted the race as a chance to knock off the man they consider the poster boy for unjust immigration detention policies.
Colorado is one of the most widely swinging battleground states. It cast its vote for Republican George W. Bush in 2004 by a higher percentage than the nation as a whole. Four years later, it did the same thing - except for Democrat Barack Obama.
That pattern is set to hold if the nation votes for Clinton. She's been leading in most polls in Colorado for most of the general election. Her campaign didn't run TV ads in the state for most of this campaign, though she has jumped in with ads in the past few days, as the race has tightened.
Only termed a swing state in the past few elections, Colorado has been shifting to the left rapidly. This year, for the first time in decades, Democratic and unaffiliated voters outnumber Republicans.
The state's growing Latino population, more than 20 percent, as well as the Denver area's explosion of younger voters are among the reasons for the shift.
Yet, like other Western swing states, Colorado is starkly divided, with a strong conservative streak as well.
If Clinton wins Colorado, it will be the first time in a century Colorado has voted for the Democratic nominee for president three times in a row.
The Sunshine State is once again the center of the presidential campaign and has been a frequent stop for Clinton and Trump. Florida is essential to Trump's chances. Barring big upsets elsewhere, failure to win here blocks the Republican's path to the 270 electoral votes he needs to capture the White House.
Clinton and Trump have focused especially on winning Central Florida, which stretches east to west from Daytona Beach on the Atlantic Coast and ending in Tampa. Democrats are buoyed by record-high early voting by Latinos fueled primarily by an influx of Puerto Ricans fleeing the island's economic difficulties. Across Florida, more Latinos had voted by Wednesday than during the entire early voting period in 2012, according to the Clinton campaign.
The politics of South Florida are also shifting as young Cuban Americans buck their elders and align with Democrats.
The state's closely watched U.S. Senate race pits Sen. Marco Rubio (R-Fla.), who used his presidential campaign to trash Congress, against Rep. Patrick Murphy (D-Fla.). Rubio has surged ahead, and Democrats have pared back ad spending, but Murphy could be helped if Clinton pulls far ahead of Trump.
The last Democrat to carry Georgia was a fellow Southerner, Bill Clinton in 1992, so the Peach State didn't appear particularly ripe for Hillary Clinton when the race began. But it has turned unexpectedly competitive this year.
Several recent polls have shown the contest to be within the margin of error or Trump leading by a modest margin.
Clinton is being buoyed by an overwhelming lead among black voters in Atlanta and elsewhere. She was up 89 percent to 5 percent among African Americans in an NBC-Wall Street Journal-Marist poll released last week.
The booming Atlanta suburbs have opened a possible path to victory for Democrats that does not require winning over conservative whites, the bedrock of Trump's constituency.
A key will be how well Clinton can mobilize not only African Americans but also growing populations of Latinos and Asian Americans. Some Democrats acknowledge they could be another election away from being consistently competitive.
Sensing an opportunity, the Clinton campaign stepped up investments in its ground game in Georgia in August, and a supportive super PAC is airing television ads.
Donald Trump's strength among white, non-college-educated voters could help swing Iowa to the GOP this cycle, after it voted for Obama in 2008 and 2012. Iowa is more than 90 percent white.
Trump has a five-point lead, according to a polling average of recent surveys calculated by The Washington Post. The Clinton campaign has touted its robust ground operation in Iowa, but the candidate herself has not held many rallies in the state.
Trump has faced criticism in many battleground states for implementing a late and weak ground operation and relying on operatives who lack the strategic experience to keep pace with Democrats. But in Iowa, Trump has Eric Branstad, the son of Gov. Terry Branstad. The Branstads know Iowa politics well, giving Trump a boost he doesn't enjoy in other important states.
Trump has made several appearances in the Hawkeye State in recent weeks and has frequently sent his quintessentially Midwestern running mate, Gov. Mike Pence, to campaign there.
Despite the buzz, Iowa has just six electoral college votes. Still, it is a must-win for Trump, given his limited path to the 270 electoral votes needed to win the White House.
This industrial, Midwestern state, which dealt a surprise blow to Clinton in the Democratic primary when it backed Sen. Bernie Sanders of Vermont, could be poised for another upset in the general election.
Michigan voters have not supported a Republican for president since 1988. But backlash against globalization has made trade deals a major issue in parts of the state where Trump expects to do best, especially among white, non-college-
educated voters.
With national polls tightening in the final days of the campaign, Trump's campaign has made a late play for Michigan, and Clinton and surrogates have recently increased visits in an effort to boost Election Day turnout. Both campaigns are now airing ads statewide. On Monday, Clinton will visit Grand Rapids, and President Obama will visit Ann Arbor.
With an electorate that is 72 percent white, Michigan is one of the least diverse states, meaning Clinton's demographic advantages - she is strong among minorities - could be limited. Clinton is trying to maintain her strength in the state's urban centers, particularly among black voters in Detroit. But they are key, and there are signs in early voting elsewhere that she is struggling with them.
Nevadans have voted for the winner in every presidential election since 1992. But like most swing states, Nevada is starkly divided between red and blue. The state's southern tip, home to Las Vegas and surrounding Clark County, is blue. The northern city of Reno and surrounding Washoe County are purple. And the rural towns dotting the vast expanse of desert in between are red.
Nevada is changing, though. Almost a third of the state is Hispanic, and there's a growing Asian American population as well. Democrats have worked hard to harness the state's new population in their favor, and Nevada is leading the way among Western states trending Democratic.
Nevada has an independent and libertarian streak, and Trump seems to have tapped into that. He's leading or tied in three of the past four high-quality polls, suggesting that his populist economic message is resonating with Nevadans still struggling to recover from the recession.
But early voters - a solid indicator in Nevada - favor Democrats in similar numbers to when President Obama won the state in 2012. This race looks like it could be a nail-biter.
Tiny and independent-minded, New Hampshire figures most prominently in the presidential election as the site of the nation's first primary vote, typically a few days after the kickoff caucuses in Iowa.
With four electoral votes, it's not a big prize in the general election, but it is considered a battleground because of significant Republican strength amid solidly Democratic northeastern states.
New Hampshire has voted Democratic in five of the past six presidential elections. Barack Obama took the state by about 5.5 percentage points over Mitt Romney in 2012, but Clinton looks unlikely to match that margin.
The Democrat has suffered a reversal of fortune in New Hampshire in polls over the past two weeks, falling to a two-point lead over the weekend, according to a poll average calculated by The Washington Post.
Some polls suggest a strong effect from the announcement on Oct. 28 of a renewed FBI inquiry into Clinton's State Department email. She is expected to return to New Hampshire for a final rally Sunday.
In addition, Obama will travel to the state on Monday on the eve of the election - a sure sign that it is closer than Clinton would like.
The Land of Enchantment has been a Democratic stronghold during the past two presidential elections, with Obama winning by double-digit margins both times. Trump recently visited the state for an evening airport rally as part of an 11th-hour attempt to put it in play. But not a single public poll has shown Clinton trailing the Republican nominee there.
Trump's anti-immigrant rhetoric and repeated vows to build a wall along the U.S.-Mexico border have made him deeply unpopular among Latino voters. That presents a major challenge for him in New Mexico, where exit poll data showed the electorate was more than a third Hispanic in 2012.
Clinton has been taking no chances with New Mexico down the stretch, opting to air ads in the state during the final week for the first time in the general election.
Democrats have won five of the past six presidential elections in New Mexico. George W. Bush narrowly won here in 2004.
One potentially complicating factor for Clinton and Trump: Libertarian Party nominee Gary Johnson served two terms as governor and has pockets of support. The most recent poll showed Johnson attracting 7 percent of the vote.
North Carolina has been one of the most heavily traveled states on the campaign trail this year and could tip either way.
The state has historically been favorable turf for Republicans in presidential races. Obama narrowly carried the Tar Heel state in 2008 but lost by a close margin to GOP nominee Mitt Romney in 2012.
Democrats see longer-term trends in the state working in their favor: an influx of white, college-educated professionals along an urban and suburban corridor stretching from Raleigh to Charlotte, and an uptick in the African American share of the electorate - part of the legacy of Obama's campaigns.
To win in North Carolina, Clinton has been banking on an Obama-like turnout from African American voters. According to exit polls, African Americans accounted for about 18 percent of the electorate in 1996. By 2012, the black share of the vote rose to 23 percent. But early voting among that group got off to a slow start this year, raising a flag about enthusiasm.
Donald Trump is trying to drive up turnout in rural North Carolina, including the east, where tobacco was once king and where the state is still suffering from manufacturing losses.
This Rust Belt state's demographics play to Donald Trump's strengths, with a population that is about 80 percent white - and heavy with working- and middle-class Americans who are anxious about the economy.
Although Obama carried the state in the 2008 and 2012 elections, Ohio has consistently polled in Trump's favor this cycle. After briefly falling to a tie in some polls in mid-October, Trump now leads Clinton by five percentage points, according to a polling average calculated by The Washington Post.
Republicans are bullish that Trump will carry the state, which is a must-win if Trump hopes to take the White House. His considerable strength among white voters in the state, especially those without college degrees, is also bolstered by his double-digit strength among men.
(Trump and Clinton appear to be tied with women voters, according to a recent Quinnipiac poll.) The Clinton campaign has made an aggressive push in Ohio in the final days of the election, hoping to compel enough nonwhite voters to cast ballots to stave off a Trump victory. On Friday night, musicians Beyoncé and Jay Z headlined a concert in Cleveland to get out the vote.
With a large population of working-class and middle-class whites, Pennsylvania is an attractive yet elusive prize for Republicans despite having voted Democratic in the past six elections.
Trump has sought to energize the Republican part of the state, which, in past elections, has been outvoted by solidly Democratic Philadelphia in the east and the area around Pittsburgh in the west. Clinton has focused primarily on those two large urban areas this year.
For Democrats, winning Philadelphia has become the key to holding Pennsylvania, and doing so means motivating the large African American population in the city along with whiter suburbs at the periphery. Those "collar counties" have held appeal for Republicans in past elections but have not given Trump much hope this year.
In 2008, Obama won nearly all of the Philadelphia suburbs atop the most populous urban areas.
A polling average calculated by The Washington Post gives Clinton a five-point advantage, but her campaign may see signs of trouble. She is campaigning twice in the state in the closing days of the race, and Vice President Biden, a Pennsylvania native, was spending the entire weekend there on her behalf.
Utah, a red state that hasn't chosen a Democrat for president since 1964, isn't likely to do so on Tuesday. But it could be the only state to hand a loss to both Clinton and Trump, thanks to a former CIA agent.
Evan McMullin, a Utah-born Mormon, is running for president as an independent. He claims to be competitive in 34 states, either on the ballot or as a write-in candidate. Utah is his best chance at becoming the first third-party candidate in 92 years to win a state. Some polls have shown him tied with Trump here, with Clinton not far behind.
McMullin's surge reflects the qualms of Utahns, many of them Mormons, about voting for Trump, a brash, thrice-married New Yorker who has made lewd comments about women and wants to bar Muslims from the country. To take advantage, Clinton opened a campaign office and dispatched surrogates.
Mitt Romney, who won Utah with nearly 73 percent of the vote in 2012, strongly disavowed Trump. Others have tried walking a finer line. After a tape emerged of Trump bragging about groping women because he is a "star," Rep. Jason Chaffetz, R-Utah, said he could no longer endorse him. Nineteen days later, Chaffetz said he would vote for Trump.
Although Virginia is considered a swing state, for months Clinton had such a comfortable lead that both campaigns went off the airwaves in the summer. But polls have tightened, and both Clinton and Trump are back on TV, and Trump is scheduled to make a last-minute visit on Sunday.
Clinton's running mate, Sen. Tim Kaine of Virginia, will return to his home state the day before Election Day to try to shore up support among African Americans and others in Richmond, where he was once mayor, and in the Northern Virginia suburbs of Washington, a fast-growing region that is rapidly diversifying and trending Democratic.
Clinton has several advantages, including strength among suburban college-educated women, a sizable portion of the electorate in Fairfax, Loudoun and Henrico counties. And she stands to benefit from higher enthusiasm among Latinos in the state.
Trump has sought to bolster his support among rural voters and made an appeal to the state's heavy presence of active-duty and military veterans.
Obama carried the state in 2008 and 2012. A Democratic win could cement Virginia's status as a blue state in presidential races.
The state where the Republican Party was formed has not gone to the GOP nominee for president since 1984, but Trump is making a last-minute and unsteady push to try to turn the state red.
Trump had planned to campaign in the state Sunday but abruptly canceled his trip the day before. He had included Wisconsin in his $25 million multistate advertising investment during the final week of the campaign.
Clinton's running mate, Sen. Tim Kaine of Virginia, will barnstorm here Sunday as Democrats hope to maintain the lead they have built.
Trump is wagering that his crusade against sweeping multinational trade deals will boost turnout among conservative white, working-class voters who have experienced firsthand the decline of the manufacturing industry in the United States.
Wisconsin is the home state of Republican National Committee Chairman Reince Priebus and Speaker Paul D. Ryan. The latter has had a rocky relationship with Trump throughout the campaign.
The last time Clinton and Trump faced voters in Wisconsin, neither experienced much success: Both lost by double-digit percentage margins to opponents during the primary.
Thirteen survivors were treated at hospitals.