Washington: After a long and bitter campaign, Americans will cast their votes on Tuesday in elections that could sweep Democrats from power in Congress and slam the brakes on President Barack Obama's legislative agenda.
Anxiety over the stumbling economy and discontent with Obama and government in Washington have propelled Republicans to the threshold of huge gains that could give them a majority in the House of Representatives and perhaps even the Senate.
Opinion polls and independent analysts project Republican gains of at least 50 House seats, far more than the 39 they need to take control and topple Democratic House Speaker Nancy Pelosi from power.
Republicans are also expected to make big gains in the Senate, although it appears more difficult, but not impossible, for them to pick up the 10 seats they need for a majority.
Obama won office two years ago on a wave of hope he could lead the United States out of a deep economic crisis, but persistent high unemployment and a gaping budget deficit have turned many voters against him.
The public mood gave rise to the political phenomenon of the Tea Party, a conservative grass-roots movement wary of Obama that backed less government, lower taxes and reduced spending.
Republican control of even one chamber of Congress would likely spark a long bout of legislative gridlock, weakening Obama's hand in fights over extending the Bush-era tax cuts and passing comprehensive climate change or immigration bills.
Republican candidates have pushed an agenda of spending cuts, deficit reduction and the repeal of at least portions of the health-care overhaul, but Obama would wield veto power over Republican initiatives.
Polls open before dawn in some areas of the eastern United States and will start to close at 6 pm but it will be hours before results are known in many crucial races.
All 435 House seats, 37 Senate seats and 37 state governorships are at stake in Tuesday's voting. Many states have been conducting early and mail-in voting for weeks.
Dozens of races are considered too close to call. Candidates in both parties launched a frenetic round of last-minute campaign stops and fund-raising appeals on Monday.