The US election will determine the balance of power in Congress and shape the future of Donald Trump's presidency, after a divided campaign that saw differences over racism, immigrants and other issues.
The country's first nationwide election since Trump won the presidency in 2016 will be a referendum on the Republican president, who has polarized the country and his hardline policies. It will also test the Democrats' ability to transform the opposition's liberal anti-Trump energy into a ballot box victory.
"All that we have achieved is at stake tomorrow," Trump told his supporters on Monday evening in Fort Wayne, Indiana, in one of three popular meetings to encourage voters to participate.
All 435 seats in the House of Representatives, 35 in the Senate and 36 in the midterm elections, which focus on competitive races from the far east to the far west, are contested by opinion polls. Either way.
Democrats are likely to get at least 23 additional seats needed to win the majority, which will enable them to block Trump's legislative agenda and investigate his administration's actions.
Republicans are expected to keep their small majority in the Senate, which is no more than two seats now, which will allow them to retain the power to approve Supreme Court appointments and other judicial nominations.
Democrats are also threatening to restore the positions of governors in several states, including Michigan, Wisconsin and Ohio, which will support the party in these states in the upcoming presidential elections in 2020.
In a last-minute spat, NBC, Fox News and Facebook pulled out a Trump campaign ad, which critics called racist.
The 30-second ad features footage of an illegal immigrant from Mexico convicted of killing two police officers in 2014, along with footage of immigrants from Mexico.
Experts expect voter turnout to be the highest in mid-term elections 50 years ago.
