(CNN) - It's election day in a once little-talked-about contest to fill a vacant congressional seat in upstate New York, that is now firmly in the national political spotlight.
And over the past month, the race in New York's 26th congressional district between Republican state Assemblywoman Jane Corwin, Democrat Kathleen Hochul, the Erie County clerk, and Jack Davis, a once-conservative Democrat who is running as a so-called tea party candidate, has to a degree turned into a proxy battle on House Republican plans to alter Medicare.
When it comes to Medicare, some national Democrats see this contest as a testing ground for next year's elections. But national Republicans disagree, saying the reason the contest between the Democratic and Republican candidates is close is because of the inclusion of the third party candidate.
The Democratic and Republican candidates have been using the issue to attack each other, and both campaigns, party committees, and outside groups have flooded the airwaves with television commercials, with many of the ads spotlighting the political battle over House Budget Chairman Paul Ryan's plan to dramatically cut federal spending by reforming Medicare.
"Jane Corwin has 100 percent embraced the Paul Ryan budget. Even when Republicans in Washington walk away from it, she's been asked again and again and she continues to support it," Hochul told CNN.
"I think it boils down to score tactics used on my opponent's part. She's trying to put out the idea that I'm trying to end Medicare. There's nothing further from the truth, I'm working to protect Medicare," responded Corwin.
The winner of the May 24 special election will fill the seat of Republican Rep. Chris Lee, who quickly resigned in February hours after the gossip website Gawker posted a shirtless photo and e-mails from the married congressman soliciting a date with a woman through the website Craigslist.
This should be a safe seat for the GOP. It's been more than four decades since a Democrat was elected to the seat, and Lee won re-election by a three to one margin last November. In 2008, Republican presidential nominee John McCain won the district by six points, the third straight presidential contest in which the GOP carried the district, which stretches from the suburbs of Buffalo east to the suburbs of Rochester.
A Siena College poll released Saturday indicated Hochul with a four point advantage over Corwin among likely voters, but the margin was within the survey's sampling error. According to the poll, 42 percent of likely voters backed Hochul, with Corwin at 38 percent and Davis at 12 percent.
Two of the top non-partisan political handicappers, the Cook Political Report and the Rothenberg Political Report, last week changed their ratings of the race: Cook to "toss up" and Rothenberg to "toss up/lean Democrat."
The Siena survey also indicates that a majority of voters in the district say the most important issue to them is Medicare, over the budget deficit and jobs.
Last week House Majority PAC, an independent Democratic leaning group, went up with an ad that claims that "Corwin's plan would essentially end Medicare" and that seniors would "sacrifice."
Their commercial went up one day after Corwin's campaign went up with a commercial attacking Hochul on Medicare.
"Kathy Hochul: A false campaign about Jane Corwin's position on Medicare when the truth is it's Hochul who says she would cut Medicare and Social Security."
Hochul's campaign, the Democratic Congressional Campaign Committee, the National Republican Congressional Committee, and American Crossroads, an independent group that leans Republican, have also gone up with commercials in the district. Overall, more than $4.3 million has been spent on running ads in this election battle, according to an analysis by Kantar Media/Campaign Media Analysis Group, CNN's consultant on political and issue advertising.
"New York-26 is looking like a proving ground for 2012 Medicare and budget debates, parties and outside groups are not going to miss their chance to get in the act," says Evan Tracey, president of CMAG and a CNN consultant.
Top House Democrats say the close race is evidence that House Republicans' support for a proposal to dramatically change Medicare is already hurting GOP candidates with voters. Asked about the impact of the Medicare issue on the New York race, House Democratic Leader Nancy Pelosi of California said recently the contest "certainly is a race that was not in play and now it is."
Massachusetts Democratic Rep. Ed Markey was more blunt, predicting the issue is producing blowback for Republicans not just in New York.
"Medicare has razor-blade-sharp edges and it's drawing political blood in New York, as it's going to across this country," Markey said.
The House Republican 2012 budget, authored by Paul Ryan, passed the House last month without a single Democratic vote and included a proposal to overhaul Medicare. Under the plan, the government would no longer directly pay medical costs for those 55 and younger, but instead would offer subsidies for seniors to use to get private health insurance coverage. A recent CNN/Opinion Research Corporation poll indicated that 49 percent of Americans prefer President Obama's approach on Medicare, with four in ten favoring the GOP proposals on Medicare.
Republicans disagree that the race is close because of Medicare.
"This race is about the fact that this is a three-way race," House Majority Leader Eric Cantor said Monday. "I do not think it can be seen as a signal as to the role of the budget reforms that we have proposed including that in Medicare. I know this town loves to take signals from individual races," said Cantor. "I think the best signal you can take is the 63 seats we picked up in November. That was a signal that the American people were tired of the direction being taken by the other side. They were upset about the situation with jobs and they were upset about government spending. I think those issues are still front and center with the voters and especially those in western New York."
And Paul Lindsay, spokesman for the House Republicans' campaign arm, recently told CNN the race is close because of the impact of Davis, the third-party candidate.
"This race is close because Republican Jane Corwin is running against two Democrats, one of whom is deceiving voters by claiming to be a Tea Party candidate," said Lindsay, spokesman for the National Republican Congressional Committee.
There's a similar message from FreedomWorks. The independent conservative grassroots group, which has organized many of the larger tea party movement events over the past two years, last week launched a campaign to expose "Jack Davis's record as a big government liberal."
And the Tea Party Express, one of the most well known and politically active of the national tea party groups, is also mounting a campaign in the district to denounce Davis "for deceptively giving himself the 'tea party' title when he does not truly support core tea party values of the movement."
Local tea party groups also weighed in last Tuesday, holding two events in support of Corwin.
Regardless of whether Medicare the reason, or if the third party candidate's the catalyst, the battle for New York 26 has grabbed the national spotlight.
Need more proof?
Both parties have brought in some of their big guns to stump for their party's candidates.
House Speaker John Boehner and Cantor made recent trips to the district to campaign for Corwin. For the Democrats, Sen. Charles Schumer of New York, one of the Senate Democratic leaders, went to the district recently to campaign for Hochul, as did the state's other Democratic senator, Kirsten Gillibrand.
Follow Paul Steinhauser on Twitter: @PsteinhauserCNN