As of two months ago, Democratic Party officials didn’t want to invest any money at all in the special election in New York’s 26th district — they saw the Buffalo-area race as a sure loser. It’s a ruby-red district, and with a credible Republican candidate, nearly everyone in both parties assumed the race wouldn’t be especially close.

As it turns out, the outcome wasn’t especially close, but in a way that was hard to predict when the race got underway.

Much to the chagrin of Republicans, the defining issue of the special election was the House GOP’s radical budget plan, most notably the Republican drive to end Medicare and replace it with a privatized voucher scheme. Jane Corwin (R) said she supported her party’s plan, and Kathy Hochul (D) talked about little else.

When the dust settled, Hochul won by four, 47% to 43%, in one of the most reliably Republican districts in the Northeast. If this race had been held in November 2010, Corwin would have won by double digits, without breaking a sweat. But thanks entirely to Republican extremism, the political landscape has already changed quite a bit over the last six months.

Indeed, if these three paragraphs don’t make the Republican Party nervous, they’re just not paying close enough attention.

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 standard GOP talking point on this special election is to note that Jack Davis, running as a Tea Partying independent, split the right and made it impossible for Corwin to win. It’s a weak excuse. For one thing, given Hochul’s margin of victory, the results were still a disaster for the GOP, Davis or no Davis. For another, if Republicans thought a third-party spoiler made the race unwinnable, why did the national party, the U.S. Chamber of Commerce, and Karl Rove’s attack operation invest so heavily to try to win?

What we saw in Buffalo was a test — how is the public responding to the GOP’s far-right agenda in Congress? It’s a test Republicans failed.

Those vulnerable GOP incumbents who voted to eliminate Medicare because their party leaders told them to have every reason to be nervous. These members were likely told, “Don’t worry, during your re-election campaign, the party, the Chamber, and Crossroads GPS will rally behind you in your district. Everything will be fine.”

Of course, they said the same thing to Jane Corwin. If it didn’t help her in a reliably red district, the anxiety among swing-district Republicans this morning should be palpable.

Overreach comes with consequences. The DCCC should be sending a gift basket to Boehner, Cantor, and Paul Ryan.

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Steve Benen

Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.