The plot has thickened going into Tuesday's special election in a western New York congressional district, where polls show the Democratic candidate has surged ahead of the former GOP front-runner, amid a fierce contest centered mainly on the future of Medicare.

The three-way race in New York’s 26th Congressional District is being characterized, especially by Democrats, as a referendum on the GOP proposal to replace Medicare with subsidies for seniors to buy private health insurance. The district has long been a Republican stronghold, and Democrats in Washington are hoping that a win there Tuesday would convince Republican lawmakers that the public rejects their strict austerity plan for dealing with the national debt and the deficit.

Weekend polls gave Democrat Kathy Hochul an edge over Republican Jane Corwin, who is now running four to six percentage points behind. Ms. Corwin, a state Assembly member, had been running four to six points ahead of Ms. Horchul, the Erie County clerk, as recently as late April. Former Democrat Jack Davis, running as a tea party candidate, is double-digits behind in the latest poll and is winning mainly Republican votes. Tea party activists say he is not one of them and is running as a spoiler.

The race is the first major contest since the Republican-led House approved the fiscal 2012 budget plan crafted by Rep. Paul Ryan (R) of Wisconsin – without a single Democratic vote. That plan, which includes the controversial Medicare provision, will come up for a vote this week in the Democratic-led Senate, where it is expected to fail.

A defeat of that budget bill in the Senate – and an upset defeat in New York of a GOP candidate who backs that plan – would help build pressure on Republicans to compromise on debt and deficit issues, say Senate Democratic leaders.

“We want a bipartisan agreement, and defeating the Republican budget and showing the weakness of its support [among the public] is one of the most important steps to move in that direction,” said Sen. Charles Schumer (D) of New York, in a conference call with reporters on Monday.

Such a narrative, Republicans say, overlooks other factors in the race, especially the role of the so-called tea party candidate as a spoiler, dividing the Republican vote.

“This race is competitive because a phony tea party candidate is spending millions of dollars purposefully confusing voters in an attempt to split the Republican vote,” said Jonathan Collegio, a spokesman for American Crossroads, a conservative nonprofit 527 organization founded by former Bush advisers Karl Rove and Ed Gillespie.

In the last weeks of the campaign, American Crossroads poured some $700,000 in television and Internet ads, direct mail, and phone calls into slamming “millionaire career candidate” Davis and Hochul on support for raising taxes.

“The Republican outside groups didn’t sound the alarm fast enough to make a difference,” says Nathan Gonzales of the Rothenberg Political Report. “Now, there’s so many messages and ads on the air that it’s an incredible clutter. If Crossroads had come in a month ago, they probably could have dramatically increased Corwin’s chances of winning the race.”

He adds: “Any election focused on Medicare will be a losing election for Republicans, but I don’t think we needed a special election in New York to tell us that. Democrats will try to take New York 26 and use it as a blueprint for races nationwide, but there are too many other factors in that race that make it difficult to extrapolate to other races nationwide.”

Each party got out its big guns in last-minute robo-calls on Monday, in a bid to their respective 26th district voters out to the polls in force on Tuesday.

"You can count on Kathy to say 'no' to partisan politics that would end Medicare as we know it to pay for more tax cuts for multimillionaires,” former President Bill Clinton said in a taped message. Back in May 2010, Mr. Clinton helped Rep. Mark Critz (D) of Pennsylvania pull out a victory in a special election that was also viewed as a bellwether race.

The Republicans tapped GOP rising star Gov. Chris Christie of New Jersey. “We're in critical times for our country, and Washington needs stand-up leaders who will fight to control spending and change business as usual,” said Governor Christie. Unlike Clinton, he did not specifically mention Medicare.