WASHINGTON Republican gains in Congress could have a profound effect on policy, from climate change legislation to the budget deficit.
Republicans will take control of the House of Representatives and have a much stronger position in the Senate in 2011 after voters on Tuesday punished Democrats over concerns about the weak U.S. economy.
Here are some questions and answers about how Congress, with stronger Republican influence, could handle key issues:
HOW WILL REPUBLICAN CONTROL AFFECT THE AGENDA?
The party that controls the House holds crucial power, taking the lead in writing bills and deciding which to bring up for a vote and when. A Republican House could pass legislation, such as promised tax relief, on simple majority votes without any Democratic support.
Democrats will still hold the Senate, but Republicans will have a much stronger position and more leverage in negotiations thanks to their party running the House. Democrats also lack the 60 votes necessary in the Senate to stop a procedural hurdle known as filibuster, which gives Republicans power to block legislation.
The split between the House and the Senate is likely to cause gridlock, and analysts say Congress might only pass mandatory spending bills and non-controversial measures.
WHAT ARE SOME REPUBLICAN PRIORITIES?
House Republican leaders will push their "Pledge to America," a governing agenda they say would create jobs, cut taxes and shrink government.
While short on specifics, the plan calls for saving $100 billion next year by scaling back spending to 2008 levels (with exceptions for the elderly and U.S. troops), ending government control of mortgage giants Fannie Mae and Freddie Mac and imposing a freeze on federal hiring. Although Obama is unlikely to sign many or any of the Republican proposals into law, they set markers in what could be a rough fight in the final two years of his presidential term.
WHAT HAPPENS TO TAXES?
Tax cuts brought in by former President George W. Bush run out at the end of 2010, on the watch of the current Congress that ends its term in December.
If lawmakers fail to extend the cuts due to partisan differences, Republicans are certain to try to renew them in early 2011 once the new Congress starts.
Obama and most Democrats want to renew tax cuts only for individual annual incomes below $200,000 and for family incomes below $250,000. Republicans want to extend all of the tax cuts, including for any income above those levels.
WILL REPUBLICANS REPEAL OBAMA'S HEALTHCARE LAW?
Republicans will not have the votes to override an Obama veto of any legislation to repeal his healthcare reform. But they could try to cut off funding to prevent full implementation of the landmark program, which passed Congress without Republican support.
Republican John Boehner, in line to become House speaker after his party's win on Tuesday, recently said he was committed to do everything he can to overturn the reform.
But Ethan Siegal of the Washington Exchange, a private firm that tracks Congress for investors, said: "It's going to be very difficult for Republicans to defund, defang, kill or impede healthcare reform legislatively."
HOW WILL CONGRESS TACKLE THE DEFICIT?
A presidential panel is set to make recommendations on December 1 on tackling a budget deficit of $1.3 trillion for the fiscal year to September 30. With voters alarmed about the U.S. fiscal gap and the pace of federal spending, the deficit debate is certain to get renewed attention next year. Republicans favor spending cuts over tax hikes but some deficit hawks say everything should be on the table. Among possible solutions: cutting retirement benefits, reforming federally funded healthcare programs, and reforming the tax code.
WHAT HAPPENS TO OBAMA'S WALL STREET CRACKDOWN?
Republicans want to roll back the landmark Wall Street reforms enacted in July but tinkering around the edges may be all they can muster.
Analysts see little to no chance of a full dismantling of the law meant to prevent a repeat of the 2007-2008 financial crisis that set off the worst U.S. recession in generations.
Republicans are targeting specific provisions of the reforms, such as funding for the new consumer watchdog. On such narrow issues, they might get some traction.
Republicans could be positioned to reverse Democrats' already stalled drive for comprehensive climate control legislation.
The Republican takeover of the House and the party's gains in the Senate will make it harder -- if not impossible -- for Obama to win legislation imposing mandatory reductions of greenhouse gas emissions from smokestacks and tailpipes.
Obama would still have the regulatory power to steer the country away from polluting fuels such as coal and oil but Republicans could counter by trying to deny funds.
WHAT ABOUT INVESTIGATIVE HEARINGS?
Republicans will take over the chairmanships of powerful committees in the House that can hold investigative hearings into administration actions, from the war in Afghanistan to the cleanup of the BP oil spill.
Republicans promise plenty of hearings, including some into Obama's $814 billion economic stimulus plan.
ANY SIGN OF ENERGY LEGISLATION?
Congress might manage to pass a bill this year to reform offshore oil drilling practices in the wake of the BP spill in the Gulf of Mexico. If it does not, the effort likely would be revived next year but again face hurdles.
A more heavily Republican Congress could see a renewed push to open drilling in protected areas like Alaska's wilderness.
Republicans will push for more government support for the nuclear power industry. One bill with bipartisan support that could advance: legislation requiring electric utilities to generate 15 percent of their power from renewable sources such as solar, wind, geothermal and hydroelectric by 2021.
(Additional reporting by Richard Cowan and Kevin Drawbaugh)