A vital vote for Donald Trump takes place today in Ohio, and the result could shape the future of the United States.
The small and seemingly insignificant race in America's Midwest could be the clearest signal yet of whether the US President will survive another term.
It is part of a flurry of critical votes that could indicate how November's midterm elections play out — and therefore whether Mr Trump will keep Congress on his side.
What's happening in Ohio?
A special election is taking place in Ohio's 12th congressional district to find a replacement for Republican Pat Tiberi, who resigned to move into business.
The nominees are Democrat Danny O'Connor, 31, a law graduate and local official, and Republican Troy Balderson, 56, a former car dealer and state senator.
While the GOP has held the seat for 35 years, the contest is neck-and-neck. While the odds remain slightly in favour of the Republicans, the Democrats have narrowed the gap to virtually nothing.
A FiveThirtyEight poll placed the district at 14 percentage points more Republican-leaning than the nation. A loss here would be an ominous for the party.
Why it's so important?
This run-of-the-mill contest between two fairly conventional candidates could tell us what to expect in the midterm elections for the House of Representatives and the Senate.
That will determine whether Mr Trump remains able to push policy through Congress, where both the upper and lower house are currently controlled by the Republican party.
The Democrats will need to win 23 extra seats to take control of the House of Representatives and gain the ability to defeat his agenda.
Candidates in close races across the country are watching "canary in the coalmine" Ohio closely for clues as to what they should expect.
The GOP has poured money into the race, and Mr Trump has shown he knows the importance of today's result, holding a huge rally for Mr Balderson in the district on Saturday night.
The President backed the nominee in a tweet, calling Mr O'Connor "weak" on crime, border, immigration and veterans, and likely to reverse tax cuts.
What will the results tell us?
If Mr O'Connor wins, or even if Mr Balderson wins by just a slim margin, Mr Trump and his party will be extremely worried.
Recent polls have shown there is just a point between the two nominees — a bad sign for the President in what should be a safe Republican seat.
And the 72-year-old's own popularity is at the centre of the matter, with the President continuing to perform poorly in approval ratings.
Ohio's 12th is predominantly white but well-educated, and many of the Republicans are centrist, socially progressive and fiscally conservative.
"What's going on now in the Republican Party is the polar opposite of what they believe in," Northeast Ohio Democrat Betsy Rader told the New York Times.
Ohio's Republican governor and Trump critic John Kasich told ABC America suburban women in the state were "really turned off" by the "chaos" that surrounds the President. "It really doesn't bode well for the Republican Party because this shouldn't even be close," he said.
Mr Trump's attack on Ohio-born basketball star LeBron James has also not helped endear him to the state. The President won the state by eight points in 2016, after Barack Obama won it by three points in 2012 — but his star may be fading. In June, a Marist poll found 57 per cent of people in Ohio did not want him re-elected in 2020.
What else are we watching?
Four other states are holding standard primaries today — Michigan, Missouri, Washington and Kansas, and these could be significant, too.
Mr Trump has tweeted his support for secretary of state Kris Kobach in the race for Kansas governor.
This was against the advice of his aides, according to the Associated Press, who fear right-wing Mr Kobach could weaken the Republicans' hold on the state.
Alexandria Ocasio-Cortez, who pulled off an upset in New York in June, is supporting two progressive candidates in Kansas; a former Homeland Security official who would be the first Muslim woman elected to Congress in Michigan; and a pastor and civil right activist in Missouri.
These are nailbiting times for the GOP, with an unpopular President alienating many Republicans and galvanising the opposition.
Democrats are hoping a "blue wave" of anger at Mr Trump's divisive policies will send swing states left and erode his power before he wins another term.
With his eyes already on that prize, the commander-in-chief is — as ever — determined to succeed.