Polls show that with less than 24 hours until voters decide which party will control Congress, Republicans are making major gains in key races and closing the gap nationally, meaning voter turnout could become the key factor.

Nationally, Republicans cut the Democrats' lead to just four percentage points, down from 11 last month, according to the Pew Research Center for the People and the Press. Two other national polls found similar results.

With many key races across the country now teetering on single-digit percentage leads, both parties are wheeling out the big guns — President Bush and House Minority Leader Nancy Pelosi — to sway undecided voters, and convince others that every vote counts.

The greatest obstacle for both parties is the historical tendency for voter turnout to be mediocre — or even poor — in off-year elections. For those who do vote, both parties have put together legal teams for possible challenges.

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President Bush heads to Florida, Arkansas and Texas to rally votes for Republican gubernatorial candidates on the last day of his 10-state campaign swing.

Bush's campaign push came in so-called "red states" that he carried by a wide margin in the 2004 presidential election.

"I'm now asking you when you go forth to find fellow Republicans and say you've got a responsibility to vote, but while you're doing it, don't overlook discerning Democrats and open-minded independents," Bush shouted at a GOP rally Sunday in Grand Island, Neb.

Former President Bill Clinton also joins the campaign trail Monday, stumping for Jim Webb, the Democratic candidate for U.S. Senate in Virginia, who is locked in a tight race with Republican Sen. George Allen, one of a handful of Senate races too close to call.

Pelosi, D-Calif., vying to become the first female House speaker if Democrats win control of the House, campaigned for Democratic candidates in the Northeast on Sunday. Democrats need 15 seats to gain control of the House.

"We are thankful for where we are today, to be poised for success," Pelosi said in Colchester, Conn. "But we have two Mount Everests we have to climb — they are called Monday and Tuesday."

In Florida, Bush will campaign for Republican attorney general Charlie Crist, running to replace Gov. Jeb Bush. Democratic Rep. Jim Davis is running against Crist.

In Arkansas, the president campaigns for Republicans Asa Hutchison, a former congressman and federal Homeland Security official, who is running against Democratic Attorney General Mike Beebe. The Arkansas race is the most expensive gubernatorial campaign in state history.

Bush heads back to Texas later on Monday, stopping at a rally in Dallas for Republican Gov. Rick Perry, who leads the polls against several challengers.

On Election Day, Bush plans to vote in Crawford and then return to Washington to wait for ballot returns.

YOU DECIDE 2006: Too Close to Call Races

Virginia: Allen vs. Webb

Clinton, Gov. Tim Kaine of Virginia and former Gov. Mark Warner will attend an election-eve rally in Alexandria, Va., for Webb.

Allen has several scheduled rallies for Monday, in Vienna, Norfolk, Roanoke and Sandston, Va.

Maryland: Cardin vs. Steele

Another close race comes in Maryland where retiring Sen. Paul Sarbanes' seat is up grabs. Polls show Rep. Ben Cardin, D-Md., has a slight edge on Lt. Gov. Michael Steele, a Republican.

Steele announced he would campaign around the clock in a final push to garner votes, stooping at a late-night bowling alley, an all-night diner and a cafe early Monday. Cardin held a late-night rally on Sunday with an appearance by Clinton with several events scheduled for Monday.

Tennesee: Corker vs. Ford

The race to replace Sen. Bill Frist, a possible contender for the White House in 2008, has attracted negative campaign advertising and drawn celebrities to appear on commercials for ballot initiatives.

Republican Bob Corker is up against Democratic Rep. Harold Ford Jr., who would become the first black senator elected in the South in more than 100 years.

Missouri: McCaskill vs. Talent

Polls show a virtual tie in Missouri's Senate race. Republican Sen. Jim Talent in running for re-election against Democratic opponent Claire McCaskill.

• Montana: Burns vs. Tester

A tight race in Montana is in a tie, where Republican Sen. Conrad Burns faces Democratic challenger Jon Tester. The latest poll by Mason-Dixon Polling & Research shows each are favored by 47 percent, with percent undecided and 1 percent favoring Libertarian candidate Stan Jones.

FOX News' Wendell Goler and The Associated Press contributed to this report.

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