G.O.P. Is Poised to Seize the House, if Not the Senate

WASHINGTON — A costly and polarizing Congressional campaign heads into its closing week with Republicans in a strong position to win the House but with Democrats maintaining a narrow edge in the battle for the Senate, according to a race-by-race review and lawmakers and strategists on both sides.

President Obama campaigned for a fourth consecutive day on Saturday as the Democratic Party threw its full weight into preventing a defeat of historic proportions in an election shaped by a sour economy, intense debate over the White House’s far-reaching domestic agenda and the rise of a highly energized grass-roots conservative movement.

But Republicans have placed enough seats into play that Democrats now seem likely to give up many of the gains they made in the last two election cycles, leaving Washington on the brink of a substantial shift in the balance of power.

The final nine days of the midterm election are unfolding across a wide landscape, with several dozen House races close enough to break either way, determining whether the election produces a Republican wave that reaches deep into the Democratic ranks. In the Senate, Democrats were bracing to lose seats, but the crucial contests remained highly fluid as Republicans struggled to pull away in several Democratic-leaning states.

The candidates, political parties and a torrent of outside groups made fresh strategic investments and pumped yet another multimillion-dollar wave of television advertising into House races across the country, hoping to press their advantages across a battleground that has expanded to nearly 100 districts.

In the House, 28 Democratic seats are either leaning Republican or all but lost to Republican candidates, according to the latest ratings of Congressional races by The New York Times, while 40 seats held by Democrats are seen as tossups. To win a majority, Republicans need to pick up a net of 39 seats; to reach that threshold they will probably have to win at least 44 seats now held by Democrats to offset a handful of projected Democratic victories in Republican-held districts.

In the Senate, races for Democratic-held seats in California, Colorado, Illinois, Nevada, Pennsylvania, Washington and West Virginia are rated as tossups by The Times. Republicans seem assured of taking Democratic seats in other states, including Arkansas and Indiana, but must win at least five of the seven most competitive remaining races to seize a majority, and Democrats improved their standing in at least three of those states last week.

In the final week of campaigning, Democrats are planning new investments to protect Senator Patty Murray in Washington, while Republicans are strengthening their effort to defeat Senator Barbara Boxer of California.

Candidates began closing arguments on Saturday, reprising divisions over Mr. Obama’s economic stimulus bill and clashing over private investment accounts for Social Security, an extension of the Bush-era tax cuts and a host of domestic policies.

While the outlook is grim for Democrats in the House, according to interviews with candidates, pollsters and consultants involved in races, the field remains volatile and strong voter turnout could save some seats. Yet even by conservative calculations, Republicans are well within reach of winning back a majority they lost four years ago.

“There are Democratic candidates who still appear to be in the race, but our candidates are delivering the fatal blow,” said Representative Pete Sessions of Texas, chairman of the National Republican Congressional Committee. “If we look all across the country, we are seeing incumbent Democrats in a world of hurt.”

A wave of anxiety swept across Democrats, regardless of seniority, geographic region or whether they voted for Mr. Obama’s agenda on the hot-button issues of health care, economic stimulus or climate change legislation.

Representative Barney Frank, Democrat of Massachusetts, gave a personal loan of $200,000 to his campaign to wage his toughest fight in years.

Representative John D. Dingell, Democrat of Michigan, the longest-serving member, invited former President Bill Clinton to his district for two stops on Sunday. Representative Gene Taylor, Democrat of Mississippi, who often is a reliable vote for Republicans, struggled to defend a seat he has held for two decades.

Republicans went after Mr. Taylor with a TV ad that opens with the precise moment Mr. Taylor supported Representative Nancy Pelosi for speaker in 2007 to the applause of his colleagues on the House floor. “This is the moment Democrat Gene Taylor turned his back on us,” the narrator said, echoing a theme that has emerged in district after district.

As they face the certainty of losses, Democrats are in a sense victims of their own success after winning 55 seats and expanding far into conservative territory over the last two election cycles. Now they are trying to defy history and demographics as they struggle to hang on to the districts in a midterm election with their party in the White House.

“We’re duking it out everywhere,” said Representative Chris Van Hollen of Maryland, the chairman of the Democratic Congressional Campaign Committee.

Should the Democrats manage to hang on to the House, it would be considered a major political upset at this point.

Republicans focused their efforts heavily on the Ohio River Valley, hoping to win back a trove of districts in Indiana, Kentucky, Ohio, Pennsylvania and West Virginia. Democrats were trying to build a firewall in the Northeast, including seats in Connecticut, New York and Pennsylvania, where a strong performance could keep Republicans from repeating their 1994 sweep, when they captured 54 seats.

With time running out, leaders of both parties planned to spend the weekend in districts across the country. Mr. Obama appeared on Saturday evening in Minneapolis with Ms. Pelosi, raising $600,000 to help pay for a final burst of advertising for House candidates. As she sought to rally the Democratic crowd, she said: “When the public knows the choice, we think that we will win — we know.”

Senator Mitch McConnell of Kentucky, the Republican leader, appeared in West Virginia with the top Republican candidates, while Representative John A. Boehner of Ohio, the likely speaker if Republicans take the House, campaigned Saturday in Kentucky on behalf of Andy Barr, a Republican who is trying to upend Representative Ben Chandler, a conservative Democrat.

Yet other vulnerable Democrats continued to hang tough, and their resilience led Republicans to look elsewhere to find Democrats who had not prepared for difficult contests.

Representative Tom Perriello of Virginia, who for months has been seen by Republicans as among the most endangered freshmen Democrats, is now in a race seen as one that could go either way. Representative Ed Perlmutter of Colorado, whose district was aggressively pursued by Republicans, said he had seen his re-election prospects improve in recent weeks as voters have focused more closely on the contest, and he said he expected many of his embattled Democratic colleagues to prevail.

“I am normally an optimistic fellow, but I am also realistic,” Mr. Perlmutter said in an interview. “I have been talking to my buddies, and they are in tough races. But they are still right in it.”

Democrats are seeking to diminish their losses by mobilizing key voting blocs, particularly suburban and upper-income voters who can be motivated by concerns about Republicans returning to power in Washington and imposing a conservative, antigovernment agenda while trying to undo much of what Democrats pushed through Congress. Students and black voters, who offered crucial support in Mr. Obama’s 2008 campaign, are also important constituencies in several districts across the Midwest, Northeast and South.

“I think they are going to show up far beyond what the polling indicates, and that is the secret to winning,” said Representative James E. Clyburn of South Carolina, the No. 3 Democrat in the House, who appeared for candidates in Illinois, Indiana, Nevada, Minnesota and New York, with plans to stump in the Carolinas next week.

“What I am seeing district by district is a different result than if you are looking at the House over all,” said Mr. Clyburn, the highest-ranking African-American in Congress.

Even though Republican optimism is high in the closing days, party leaders have ordered lawmakers and candidates to avoid overconfidence.

“It’s a battle to the end,” said Representative Greg Walden of Oregon, a vice chairman of the Republican Congressional committee. “But only 20 months ago, Republicans were viewed like mold — not really alive, but you couldn’t kill us either. We’ve come back.”

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