Many of the ads are negative as Republicans hammer away at Obama, the lame duck President who leaves office in January 2016.
In an election season without a major national concern - besides widespread dissatisfaction with the Government and worries about survival in America's limp economic recovery - Obama is the default issue.
Once hailed as a transformational leader, his dismal poll ratings after six years of dashed hopes, presidential missteps and congressional gridlock, with major issues like immigration and climate change sidelined, make him a liability. Many Democrats who would normally welcome his appearance on the stump, hoping to energise their appeal, have distanced themselves from Obama.
Nonetheless, the President has defiantly placed his record on the midterm agenda, reminding Americans he hauled them back from the abyss of the 2008 global financial crisis - even though many have yet to benefit.
"Make no mistake, these policies are on the ballot. Every single one of them," the President told students at Northwestern University this month.
The President's strategy appears to be to scare enough Democrats out to vote. Traditionally, far fewer Americans vote in midterms than in presidential races. Pundits suggest turnout next week will nudge 40 per cent.
Many are likely to be white, a plus for Republicans. Obama did well in 2008 and 2012, when his formidable election team mobilised blacks and Latinos. Today, both groups feel let down: Latinos are angry immigration reform still languishes and blacks are disappointed that, despite electing a black President, who appointed a black Attorney-General, racism remains virulent.
This is evident, say critics, in states where Voter ID laws disadvantage blacks, Latinos, the poor and the elderly, a form of poll tax that evokes the Jim Crow era. Last week, the US Supreme Court decided a Texas ID law - which mandates seven forms of ID, including a passport or driver's licence - could stand, even though dissenting Justice Ruth Bader Ginsberg says this excludes an estimated 600,000 eligible Texans and is clearly discriminatory.
After casting his vote Obama insisted "exercising our franchise, that's where all of us are the same". He then raced off to a Democratic National Committee fundraiser, where attendees had forked out more than US$50,000 ($64,190) to hear him speak. Some Americans are more equal than others.
Money doesn't just talk in US elections, it screams. Two landmark Supreme Court decisions, in 2010 and in 2014, reversed four decades of restrictions to allow virtually unlimited campaign spending, either anonymously to political action committees or directly to candidates and parties. The floodgates have opened and this year's federal total is expected to eclipse US$4 billion - to critics a recipe for corruption as donors buy politicians.
In a system where checks and balances are meant to keep politicians honest, this tsunami of money fuels public cynicism while suppressing voter turnout, says Sheila Krumholz of the Centre for Responsive Politics, which tracks campaign spending. The Supreme Court decision "is further transforming an already elite system", she says.
"Less than one-half of 1 per cent of Americans give contributions of a size we can see: that's more than US$200. So the court's ruling has further concentrated power."
Tellingly, growing US income inequality - highlighted by French economist Thomas Piketty in his bestseller Capital - is not a midterm issue: the Brookings Institute has called inequality the issue that dare not speak its name. Political dynasties, which benefit from inequality as ordinary voters struggle to get ahead, also fuel elitism. This is not new - the Kennedy brand has had juice for decades - and despite the Founding Fathers' antipathy towards aristocrats, dynasties flourish, as the Bush and Clinton clans show. Several famous scions - Michelle Nunn in Georgia, Mary Landrieu in Louisiana and Mark Udall in Colorado to name three Senate hopefuls - are in tight races.
Other toss-up states cited by the Cook Political Report are Alaska, Kansas, Arkansas, North Carolina, Kentucky, Iowa and New Hampshire. Larry Sabato, director of the Centre for Politics at the University of Virginia, believes Republicans will gain a minimum four to five Senate seats.
But several safe GOP seats, including conservative heartlands Kansas and Georgia, have unexpectedly come into play, in part due to internecine warfare between Tea Party extremists and moderates.
The Huffington Post poll aggregator gives Republicans a 63 per cent likelihood of taking control of the Senate, where Democrats hold a 55-45 majority. But if the Republicans win five seats, dividing the upper chamber 50-50, the "Biden Majority" - Vice-Presidents hold a casting vote - would give Democrats an edge, with Joe Biden's vote used as a tie-breaker.
A Republican win may not end congressional gridlock. Democrats might filibuster bills, Obama can veto legislation - although he may be reluctant to kill government funding bills. And while Republicans have largely been defined by opposition to Obama, victory next week would let them lay out an agenda to prime voters for the 2016 election.
The Tea Party, however, is already a headache for GOP grandees in the House. If the radicals grab the Senate wheel this might alienate voters - a plus for Democrats in 2016.
As Commander-in-Chief, Obama has a fairly free hand with foreign policy and may be less inclined to consult with a GOP-controlled Congress.
Whether it would give him fast-track authority for the Trans-Pacific Partnership trade deal is anyone's guess. Perhaps the biggest effect of a GOP victory is Congress could nix Obama's judicial nominees, including for the Supreme Court if a vacancy appears.
There is also speculation the midterms will affect the presidential election, as suspense mounts that Hillary Clinton and Jeb Bush, from Democratic and Republican dynasties respectively, will declare.
A GOP sweep next week may embolden a big Republican field and suppress Democrats. Or not.
Two big questions loom in the wake of the midterms. Who can win in 2016? And how much will it cost? Sabato expects the bill could reach US$12 billion. But for Americans who feel shut out of federal politics, the main question is if anything will have changed on November 5.
