Q+A: Outlook for midterm elections

WASHINGTON (Reuters) - Republicans appear headed to a big victory in Tuesday's midterm elections that would deal a severe political blow to President Barack Obama and spark a shake-up in Washington with far-reaching implications.

Spurred by voter discontent with Obama and the struggling economy, Republicans are heavy favorites to capture at least the 39 Democratic seats they need to gain a majority in the U.S. House of Representatives. They could come close to picking up the 10 Democratic seats they need for Senate control.

Here are some questions and answers about the election and the impact of a Republican victory.

WHAT IS THE MOST LIKELY RESULT?

With less than a week to go, political handicappers pick Republicans to win a House majority and make big gains in the Senate but probably fall just short of the seats needed to give them Senate control.

Charlie Cook of the nonpartisan Cook Political Report has projected Democratic losses of 48 to 60 House seats. He said more than 50 Democratic House incumbents have trailed their Republican rivals in at least one poll this year.

"At this point, a Republican takeover of the House seems set in stone," he wrote.

University of Virginia political scientist Larry Sabato predicts a Republican gain of 47 House seats and eight to nine Senate 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 but not impossible task.

WHY ARE DEMOCRATS IN SUCH TROUBLE?

Democrats have faced a perfect political storm this year composed of voter worries about the economy, unhappiness with Democratic leadership in Washington and faltering confidence in Obama.

Obama's approval ratings have dipped into the low- to mid-40s, and the number of Americans who believe the country is on the wrong track has climbed to more than 60 percent in most polls.

Polls also 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. Republicans are still more enthusiastic about the election and more likely to vote than Democrats even after a recent upturn in Democratic engagement.

History is also working against Obama and Democrats. The party that controls the White House has traditionally lost seats in the midterm election in a president's second year.

WHAT KEY RACES COULD DECIDE HOUSE AND SENATE CONTROL?

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.

The Cook Report lists 91 seats held by Democrats as either highly competitive or likely to switch. Republicans have just nine seats in that category.

In the Senate, a handful of veteran Democrats facing unexpectedly tough re-election races could decide the majority, including Democratic leader Harry Reid of Nevada, Patty Murray of Washington and Barbara Boxer of California.

Republicans appear likely to hold all of their own Senate seats. They also have commanding poll leads in three Democratic-held states -- Arkansas, Indiana and North Dakota -- and a solid lead in Wisconsin.

That means to gain a majority, Republicans must string together wins in six of seven close races in California, Washington, Nevada, Colorado, Pennsylvania, Illinois and West Virginia.

WHAT WOULD REPUBLICAN LEADERSHIP IN CONGRESS MEAN?

A Republican win in either the House or Senate could mean gridlock and political conflict -- and plenty of it.

Republican majorities would slam the brakes on Obama's legislative agenda, but it would be nearly impossible to pass new initiatives without 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 would be forced to work with moderate Democrats in both chambers if they want to pass legislation -- particularly since Obama would be waiting to veto any bill that does not pass muster among Democrats.

Republican majorities would put their House leader John Boehner and their Senate leader Mitch McConnell in charge, and they would set the agendas for their chambers while trying to manage more conservative Republican caucuses.

McConnell said last week that his priority would be beating Obama in 2012. "The single most important thing we want to achieve is for President Obama to be a one-term president," McConnell told a magazine.

Republicans also would run committees and gain subpoena power that would make it easy to investigate the Obama administration and force witnesses to testify.

WHAT ISSUES WOULD A REPUBLICAN CONGRESS FOCUS ON?

On the campaign trail, Republicans have pushed lower spending, the extension of expiring tax breaks and the repeal of portions of the healthcare overhaul.

Undoing key elements of the Obama agenda -- the economic 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 could draw Republican opposition, however.

WHAT IS AT STAKE FOR THE REPUBLICAN PARTY?

Win or lose, Republicans face an internal battle over the future of the party after this year's success of the grass-roots

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.

Boehner and McConnell will attempt to manage a batch of new members whose candidacies came from the Tea Party movement and who will not be inclined to follow the dictates of the Republican establishment.

WHAT DOES IT MEAN FOR THE 2012 WHITE HOUSE RACE?

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, industry bailouts 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.

(Editing by Vicki Allen)