WASHINGTON (Reuters) – After a long and bitter campaign, Americans 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 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.
“The Democrats' economic plan is not working,” said Peter Ruiz, a Miami retiree who voted for Republicans on Tuesday despite backing Obama two years ago. “We need to try something else.”
Opinion polls and independent analysts project Republican will win at least 50 House seats, far more than the 39 they need to take control and topple Democratic House Speaker Nancy Pelosi from power. More than 90 Democratic seats are in danger, according to the nonpartisan Cook Political Report.
Republicans are also expected to make big gains in the Senate. But it will be more difficult for Republicans to pick up the 10 seats they need for a majority.
The expectations of Republican gains drove stocks higher on Tuesday on hopes of a more business-friendly Congress.
Polls will start to close at 6 p.m. EDT (2200 GMT), but it will be hours or possibly days before results are known in many crucial races.
All 435 House seats, 37 of the 100 Senate seats, and 37 of the 50 state governorships are at stake in Tuesday's voting.
Obama won office two years ago with the hope he could lead the United States out of a deep economic crisis, but persistently high unemployment and a gaping budget deficit have turned many voters against him.
“People are just fed up with the Obama administration -- that 'hope and change' thing,” said retail manager Nadine Leder in Milwaukee, Wisconsin, who planned to vote for Republicans.
The public disgust gave rise to the Tea Party, a loosely organized conservative movement that backs smaller government, lower taxes and reduced spending.
Republican control of even one chamber of Congress would likely spark legislative gridlock, weakening Obama's hand in fights over the extension of soon-to-expire income-tax cuts and the passage of comprehensive energy or immigration bills.
“We can expect very substantial Republican gains leading to super-gridlock for two years,” said University of Virginia political science professor Larry Sabato.
Stocks have been buoyed in recent months by the expectation of big Republican wins, since investors tend to view GOP policies as more favorable for business growth. That trend continued on Tuesday, even though some research suggests that stocks have languished in periods of divided government.
“I think you're seeing a lot of long positions being taken going into the election,” said Rick Meckler of LibertyView Capital Management in New York.
Republican candidates have pushed an agenda of spending cuts and at least a partial repeal of Obama's healthcare and Wall Street reforms, but Obama could veto their efforts.
Republicans, who were blamed by many voters for the devastating financial crisis that led to a deep recession, have acknowledged that they need to win back the public's trust.
“It is not the American people saying: 'We love you, Republicans.' It's the American people saying: 'Republicans, we'll give you another chance,'“ said Mississippi Governor Haley Barbour, who heads the Republican Governors Association.
Dozens of races are considered too close to call.
Traders on Tuesday were betting Democrats have a 46.5 percent chance of holding onto the Senate -- the lowest percentage in the life of the trade on InTrade, an online market that allows traders to bet on real-world events.
The election will determine which party holds the upper hand as legislative districts are redrawn at the state level following the 2010 census.
Voters on Tuesday will also weigh in on a variety of topics: in California, for example, they could approve a measure that would legalize possession of marijuana.
Photo: Barbara Ivry (L) prepares to vote at a Manhattan polling place November 2, 2010 in New York City. (Getty Images)
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