The economy has been at the centre of electoral campaigning
Millions of voters are preparing to vote in the US mid-term elections to elect a new House of Representatives and one-third of the Senate.
President Barack Obama’s Democratic party is expected to lose its majority in the House of Representatives, but may hold on to the Senate.
Republicans hope to capitalise on voter discontent with the economy.
The parties used a final day of campaigning on Monday to urge their supporters to go out and vote.
Voting is set to begin on the East Coast at 0600 EDT (1000 GMT) when the first polls open in Connecticut, Indiana, Kentucky, Maine, New York, Tennessee, Vermont and Virginia.
The end will come 14 hours later when the last poll closes in Alaska at 0000 EDT (0400 GMT).
Up for election are all 435 House seats, 37 of the 100 seats in the Senate, governorships of 37 of the 50 states and all but four state legislatures.
The Republican Party needs to gain 39 House seats to win control of the lower chamber of Congress and 10 to take over the Senate. Opinion polls have regularly predicted that the Republicans will seize the House, but the race for control of the Senate is likely to be tighter.
In addition, voters will decide on some 160 measures on the ballots in 37 states ranging from marijuana legalisation in California to a referendum in Oklahoma on forbidding judges from using Islamic Sharia law in rulings.
If Californians decide in favour of legalising marijuana possession for personal use, it will put their state at odds with federal law.
On Monday, Mr Obama tried to rally support for Democrats on Monday by giving an interview to Ryan Seacrest, host of the popular TV programme American Idol. The interview is due to air on Tuesday on Seacrest’s nationally syndicated radio show.
Mr Obama also recorded interviews for radio stations in the cities of Milwaukee, Cincinnati, Philadelphia, Honolulu and Miami.
He spent Monday at the White House, while First Lady Michelle Obama campaigned in Nevada and Pennsylvania.
Campaigning for the sitting Senate majority leader Harry Reid, Mrs Obama updated her husband’s 2008 campaign slogan: “Can we do this? Yes, we can. Yes, we must,” she told the crowd.
Republicans are riding high in opinion polls, buoyed by discontent over unemployment running near 10%, slow economic growth and a burst housing market bubble that has seen many Americans lose their homes.
The party has also gained from the backing of the populist Tea Party movement, which has given voice to conservative grassroots opposition to Mr Obama and the Democrats’ economic stimulus programmes and healthcare overhaul.
Tea Party favourite Sarah Palin, the Republican vice-presidential candidate in 2008 and a former governor of Alaska – who is not standing for office – said in a TV appearance on Sunday that Tuesday’s vote would be a “political earthquake”.
Republican House leader John Boehner, who stands to replace Democrat Nancy Pelosi as the House Speaker if the polls are borne out, acknowledged the country’s economic problems had not started under Mr Obama.
“But instead of fixing them, his policies have made them worse,” he said, campaigning in Ohio.
The results of the day’s gubernatorial and state legislative elections could also have a big impact on American politics.
In a given state, the party that controls the state legislature and holds the governor’s office has influence over the redrawing of the Congressional district map for the next 10 years.
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