Democrats scored an upset in one of New York’s most conservative Congressional districts on Tuesday, dealing a blow to the national Republican Party in a race that largely turned on the party’s plan to overhaul Medicare.
The results set off elation among Democrats and soul-searching among Republicans, who questioned whether the party should rethink its commitment to the Medicare plan, which appears to have become a liability as 2012 elections loom.
Two months ago, the Democrat, Kathy Hochul, was considered an all-but-certain loser in the race against Jane Corwin. But Ms. Hochul seized on her Republican rival’s embrace of the proposal from Representative Paul D. Ryan, Republican of Wisconsin, to overhaul Medicare, and she never let up.
Voters, who turned out in strikingly large numbers for a special election, said they trusted Ms. Hochul, the county clerk of Erie County, to protect Medicare.
“I have almost always voted the party line,” said Gloria Bolender, a Republican from Clarence who is caring for her 80-year-old mother. “This is the second time in my life I’ve voted against my party.”
Pat Gillick, a Republican from East Amherst, who also cast a ballot for Ms. Hochul, said, “The privatization of Medicare scares me.”
The district, which stretches from Buffalo to Rochester, has been in Republican hands for four decades, producing influential Republican figures like Representative Jack Kemp.
The campaign drew intense interest, with both major parties in Washington and their allies flooding the district with radio and television advertising. Total spending exceeded $6 million.
On Tuesday, Republicans were already debating the factors that shaped the outcome of the race. The mood inside a meeting of the House Republican caucus in the Capitol was anxious, and some members suggested that it would be oversimplifying to attribute the results to one cause.
Some said Ms. Corwin proved a less nimble and ultimately less appealing candidate than Ms. Hochul, who was an energetic campaigner and seemed to connect with audiences on the trail.
So, when Medicare erupted as a driving issue in the race, Ms. Corwin, a wealthy former Wall Street analyst, was knocked off balance and struggled to respond.
In the closing hours of the race, Ms. Corwin admitted as much, saying about her rival’s attacks: “When she started making these comments, I thought, ‘This is so outrageous no one would ever believe it.’ Apparently some people did.”
Others cited the presence of a third candidate, Jack Davis, who ran on the Tea Party line after failing to win the Republican nomination. Mr. Davis not only drew conservative support away from Ms. Corwin, but also turned his aggressive attacks on her in the end, contributing to her negative numbers.
And Ms. Hochul seemed genuinely well-liked by the public. As the clerk of Erie County, she oversees the autos bureaus, which issue driver’s licenses; she became more prominent in 2008 when she challenged former Gov. Eliot Spitzer’s plan to issue licenses to undocumented immigrants .
“I remember when she was in the auto bureau in Buffalo, she did a lot with the license plates,” said Jim Van Wagner, a Republican and former auto worker from Albion, adding: She’s a good one.”
Still, given the makeup of the district, one of four in the state that John McCain carried in 2008, Republicans said they needed to understand if they had misread the public.
“It’s a Republican district with a solid Republican candidate,” said Representative Peter T. King, a Republican from Long Island. “What went wrong? We definitely have to determine the extent to which the Medicare issue hurt us.”
The seat became vacant in February when Representative Christopher Lee, a Republican, abruptly resigned after he e-mailed a shirtless photo of himself to a woman and it was published on the Internet.
Top Republicans, including House Speaker John A. Boehner of Ohio and the majority leader, Eric Cantor of Virginia, traveled to the district to provide support to Ms. Corwin.
At the same time, the national party and its allies, including the U.S. Chamber of Commerce and a group tied to the Republican strategist Karl Rove, jumped in, spending at least $1.1 million on radio and television ads supporting Ms. Corwin.
Democrats brought out their heavy hitters too, including Bill Clinton, who recorded a phone message that reached homes throughout district; and Representative Nancy Pelosi of California, the House Democratic leader, who sent out fund-raising solicitations casting the race as an opportunity for Democrats to win in the backyard of Republicans.
The race also marked the debut of House Majority PAC, a group recently established by Democratic strategists as a counterbalance to the conservative organizations that helped Republicans make significant gains in the 2010 elections. House Majority PAC spent nearly $400,000 on advertising in the race.