One day before midterm elections that could usher in a new era of divided government in Washington, President Joe Biden and his predecessor Donald Trump will hold competing rallies in a final effort to mobilise supporters.
Biden, whose sagging popularity has made him unpopular in several swing states, is in the reliably Democratic Maryland on Monday, where the Democratic gubernatorial nominee, Wes Moore, is widely expected to win back the Republican-held governorship.
Trump, meanwhile, will be in Ohio to campaign alongside the Republican Senate nominee, J.D. Vance, who emerged from a crowded field of candidates on the strength of Trump's endorsement.
Weighed down by voter frustrations over rising prices, Biden's Democrats fear Tuesday's elections could see them lose control of one or both chambers of Congress.
That would spell the end of Biden's legislative agenda - including Democratic priorities such as abortion rights, family leave and climate change - and open the door for two years of Republican-led investigations that could potentially damage the White House. A Republican-led Senate could also block Biden's nominations for judicial or administrative posts.
Billionaire Elon Musk, whose purchase of Twitter has Democrats worried that it could unleash a wave of disinformation, tweeted on Monday that "independent-minded voters" should vote for a Republican Congress "because shared power curbs the worst excesses of both parties." The post stood in contrast to an April 27 tweet in which Musk said the site "must be politically neutral" to merit public trust.
If Republicans secure a House majority, they plan to use the federal debt ceiling as leverage to demand that Biden accept deep spending cuts. The US Treasury is expected to hit its $US31.4 trillion ($NZ52.8 trillion) borrowing limit in 2023, and any protracted stalemate that risks a default on the US government's debt could roil financial markets.
A Republican Congress would also seek to make the 2017 individual tax cuts passed under Trump permanent. That law slashed top-line tax rates on corporations, a permanent feature that Democrats failed to reverse with control of Congress over the last two years.
Control of Capitol Hill would give Republicans the power to block aid to Ukraine, but they are more likely to slow or pare back the flow of weapons and economic assistance to Kyiv than stop it.
Biden has warned that a Republican victory could weaken the foundations of US democracy itself. "Democracy is literally on the ballot," he said at a rally in Yonkers, New York, on Sunday.
Many Republican candidates have echoed Trump's baseless claims of fraud in his 2020 election defeat. Some of them could end up as governors or election administrators in battleground states and play a central role in the 2024 presidential race.
Trump, whose endorsements played a critical role in shaping the Republican field, remains the party's dominant figure, and he has repeatedly hinted that he plans to launch another presidential run soon.
With narrow control of the House and the Senate, Biden's Democrats helped him to fulfil campaign promises to boost clean energy, fight the Covid-19 pandemic and finance the rebuilding of some crumbling roads and bridges.
But surging inflation and concerns about high crime have led many voters to sour on his leadership. Only 40% of Americans approve of his job performance, according to a Reuters/Ipsos poll completed on Tuesday.
Despite Biden's warnings about democracy, many of his fellow Democrats have emphasized more practical matters, such as their work to lower prescription drug prices and defend the Social Security safety-net programme.
While Democrats also campaigned on abortion rights, opinion polls show that has faded as a top voter concern.
More than 40 million American have already cast their ballots, either in person or through the mail, according to the US Elections Project, which tracks early voting.
Because some states allow ballots to be mailed on election day, experts say it might be days or weeks before the outcome of some close races - and control of Congress - is clear.
Thus far, polling problems have not been widely reported. In Georgia, where one of the nation's most closely contested Senate races is unfolding, election officials acknowledged on Friday that they erroneously failed to mail 1046 absentee ballots to people who had requested them.
County officials said about half of the voters either voted early or received a replacement ballot overnight and recommended that the rest vote in person. The American Civil Liberties Union filed a lawsuit on Sunday seeking to extend the deadline to return the ballots past Election Day on Tuesday.
