Control of Congress was on the line Tuesday, hinging on whether a majority of voters are dissatisfied enough with Republican leadership to hand over the reins to Democrats on issues ranging from Iraq and the War on Terror to illegal immigration and trade deficits.

At stake in the midterm election is all 435 House seats, 33 in the Senate, 36 races for governor, ballot measures on same-sex marriage, embryonic stem cell research, the minimum wage, English language requirements, and more — plus the overarching vote of confidence in President Bush's policies in the last two years of his presidency.

A swing of 15 seats in the House or six in the Senate is needed for a change of leadership.

Both parties sent their chairmen out early Tuesday to state the Election Day party lines.

"I believe we're going to defy the experts and maintain our majority in the House and the Senate," GOP Chairman Ken Mehlman said on CBS's "The Early Show."

Democratic Chairman Howard Dean countered, "If you want change, we can give you change."

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White House press secretary Tony Snow, appearing Tuesday on Rush Limbaugh's radio show, argued that the Democrats' only stance is "literally running around and heckling the president rather than trying to think seriously about how to deal with Usama bin Laden or a global war on terror."

"You gotta wonder if they're a serious political party," Snow said. He also criticized a Democratic proposal for dealing with the Iraq war by saying, "We do, quote, phased redeployment, what we do is we invite a whole lot more September 11ths."

President Bush, meanwhile, flew to his home state of Texas to vote, finishing a restrained five-day campaign swing in mostly GOP strongholds.

Both parties sent thousands of volunteers to competitive districts to mobilize voters and assembled legal teams to watch for irregularities in balloting systems that continue to be error-prone six years after the hanging-chad debacle of 2000.

The Justice Department sent a record 850 poll watchers to 69 cities and counties to safeguard against fraud, discrimination or system malfunctions in tight races.

Republicans have been the acknowledged champions at getting supporters out to polling stations, a critical skill in midterm elections when turnout is typically low -- around 40 percent -- and one that heightened suspense over which party would hold the levers of power at the end of the counting.

At least two dozen Republican House seats were at risk.

Among GOP-held open seats, polls show those in Arizona, Colorado, New York, Ohio and Iowa appeared most vulnerable. Republican Reps. John Hostettler, Chris Chocola and Mike Sodrel of Indiana; Charles Taylor of North Carolina; Curt Weldon, Don Sherwood and Melissa Hart of Pennsylvania; and Charles Bass of New Hampshire were in particularly difficult re-election struggles.

In Senate races, Republican incumbents Mike DeWine in Ohio and Rick Santorum in Pennsylvania appeared to be facing the toughest fight; Sens. Lincoln Chafee in Rhode Island and Conrad Burns in Montana each were given a good chance against stiff competition.

Rep. Nancy Pelosi of California, in line to become the first woman speaker in history if Democrats win control of the House, was in Washington after a weekend of campaigning for candidates in Pennsylvania and Connecticut.

The campaign's final hours brought fresh evidence of the enormous cost.

Spending by the two national parties surged in the final week as Democrats and Republicans invested in television commercials designed to sway the outcome in more than 60 House races and 10 Senate contests. In all, the two parties have spent about $225 million thus far in campaign activities independent of the candidates themselves.

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