Americans voted today in elections for Congress that could curb the power of George W. Bush's Republicans, force a change of direction in Iraq and shape the legacy of a US president with two years left in office.
President George W. Bush and first lady Laura Bush at a Republican Party congressional mid-term election campaign rally in Florida
Democrats are on course to recapture control of the US House of Representatives from Republicans for the first time since 1994, opinion polls showed, with their chance of taking over the Senate hinging on several key races that are too close to call.
A majority for the party in even one chamber of Congress could slam the brakes on Bush's second-term legislative agenda, hasten his lame-duck status and give Democrats a chance to investigate his most controversial policy decisions, such as the war in Iraq.
Polls opened at 6am in some areas of the eastern United States and will start to close at 6pm, but it could be hours before results are known in many crucial races.
Officials and experts reported electronic voting machine malfunctions in Indiana, Ohio, New Jersey, Colorado and Florida, but many of the problems were minor and temporary.
After a five-day swing through 10 states to fire up supporters in Republican strongholds, Mr Bush cast his ballot near his ranch in Crawford, Texas, and urged all Americans to vote no matter which side they backed.
All 435 House seats, 33 Senate seats and 36 governorships are at stake and Democrats need to pick up 15 House seats and six Senate seats to seize control of both chambers. About 50 contested House races and 10 Senate races are the chief battlegrounds.
Independent analysts predict Democrats could gain 20 to 40 House seats, while polls show races for Republican-held Senate seats in Missouri, Virginia, Tennessee, Montana and Rhode Island are too close to call.
Democrats probably need to win four of those five Senate races to take control of the chamber. Two national opinion polls on Monday showed Democrats still held a double-digit advantage when likely voters were asked which party's candidate they would support.
The new polls contradicted two surveys released on Sunday that showed Republicans closing the gap on Democrats. History was with Democrats -- the party holding the White House traditionally loses seats in a president's sixth year.
The battle for the House will be fought largely in the East and Midwest, where scores of Republican incumbents are fighting for their political lives amid what polls show is a strong desire for change.
At least three Republican incumbents face strong challenges in Indiana and Connecticut, while four Republican-held seats in Pennsylvania and five New York seats could fall to Democrats. In a campaign dominated by Iraq, Mr Bush defended his handling of the war to the end, despite his low job approval ratings and growing public discontent.
He questioned what Democrats would do differently and predicted Republicans would retain control of Congress. "We have a plan for victory. We've got a strategy to win," Mr Bush told a rally in Bentonville, Arkansas on the eve of the election. "I knew we were going to finish strong."