WASHINGTON, Sept 8 (Reuters) - A Republican win in even one chamber of the U.S. Congress in the Nov. 2 midterm election would create a huge shake-up in Washington, with far-reaching implications.
Republicans are growing favorites to capture the 39 Democratic seats they need for a House of Representatives majority, and could even pick up the 10 Democratic seats they need to gain Senate control.
Here are some questions and answers about the election and the impact of a potential Republican victory.
With two months to go, political handicappers are picking Republicans to narrowly win a House majority and make big gains in the Senate, although not enough to give them control.
Charlie Cook of the nonpartisan Cook Political Report wrote Tuesday that his race-by-race analysis showed Republicans are poised to gain at least 40 House seats and possibly more.
"The House has reached the tipping point," Cook wrote.
University of Virginia political scientist Larry Sabato raised his prediction for Republican gains last week to 47 House seats.
In the Senate, Cook predicts a Republican gain of seven to nine seats. Republicans must retain their own Senate seats and sweep nearly all of the competitive Democratic seats to win control, a difficult.
Worries about the economy, unhappiness with Democratic leadership in Washington and plummeting confidence in President Barack Obama have created a perfect political storm.
Obama has seen his approval ratings slide well below 50 percent over the summer, while the number of Americans who believe the country is on the wrong track has climbed to above 60 percent in most polls.
Most polls show the sweeping healthcare overhaul passed by Democrats in Congress remains unpopular with a majority of Americans, and public dissatisfaction with congressional Democrats is widespread.
Obama's popularity among independents, a crucial bloc that backed him in 2008, has dipped below 50 percent in many polls, and Republicans are more enthusiastic about the election and more likely to vote than Democrats.
Obama and Democrats got no help last week from the latest jobless report, which showed the unemployment rate inching up to 9.6 percent.
In the House, Democrats elected in Republican-leaning districts in 2008 with the help of a heavy Democratic turnout fueled by Obama's candidacy are struggling to hold their seats in the face of a growing Republican wave.
The fate of first-term Democratic incumbents like Virginia's Tom Perriello, Colorado's Betsy Markey, Ohio's John Boccieri and Florida's Alan Grayson could be crucial to the balance of power.
In the Senate, a handful of veteran Democrats facing unexpectedly tough re-election races could decide the outcome, including Democratic leader Harry Reid of Nevada, Russ Feingold of Wisconsin, Patty Murray of Washington and Barbara Boxer of California.
Democrats are keeping an eye on two races they thought would be cakewalks, the Connecticut battle for retiring Democratic Senator Chris Dodd's seat and the election to replace late West Virginia Senator Robert Byrd.
If Republicans pull a surprise win in either state it could be the end for Democratic Senate hopes.
A Republican win in either the House or Senate, or both, could mean gridlock and political conflict -- and plenty of it.
Republican majorities would slam the brakes on Obama's legislative agenda, but would find it nearly impossible to pass new initiatives that did not have considerable Democratic support.
Even if Republicans muscled partisan bills through the House, Democrats in the Senate would be able to block them through either majority votes or a procedural tactic that takes 60 votes to overcome.
That could mean Republicans will be forced to work with moderate Democrats in both chambers if they want to pass legislation -- particularly since Obama will be waiting to veto any bill that does not pass muster among Democrats.
Republican majorities would put House leader John Boehner and Senate leader Mitch McConnell in charge, and they would set the agendas for their chambers while trying to manage more conservative Republican caucuses.
Republicans also would run committees and gain subpoena power that would make it easy to investigate the Obama administration and force witnesses to testify.
On the campaign trail, Republicans have pushed lower spending, the extension of expiring tax breaks and the repeal of the healthcare overhaul.
Undoing key elements of the Obama agenda -- the stimulus spending and the healthcare bill -- would be a high Republican priority. Democrats, however, probably would have enough backing to block the moves in the Senate, and Obama would veto the effort anyway.
On foreign policy, Obama's troop escalation in Afghanistan drew support from most Republicans, with the prime opposition coming from his fellow Democrats. His planned troop withdrawal next year would likely draw Republican opposition, however.
A Democratic loss would be a bruising blow to Obama, who entered the White House with high public hopes in January 2009. He has helped push through Congress a broad economic stimulus bill and ambitious overhauls of the healthcare system and financial regulations.
But the loss also would free Obama to engage in direct battle with Republican congressional leaders and presidential contenders, giving him a new set of political foils and somewhere else to point the finger of blame when things go wrong.
Obama would have a role model in former President Bill Clinton, a Democrat who saw Republicans capture Congress in a 1994 sweep two years into his term.
But Clinton easily won re-election in 1996 after moving to the center and winning a budget showdown with Republican House Speaker Newt Gingrich over the closing of the federal government.
Win or lose, Republicans face an internal battle over the future of the party after this year's success of the grassroots conservative "Tea Party" movement.
The movement, which favors limited government, low taxes and less government spending, could be well represented in the new Congress and push the party and its presidential contenders to the right.