The Senate Democratic majority decided to strike while the iron was hot. The House Republicans’ plan to end Medicare had just cost the GOP a previously-“red” House seat, and public opposition to the idea keeps growing. It was time, Dems decided, to force Senate Republicans to take a stand on the politically toxic agenda.

But when the vote was held, nearly all of the Senate GOP stuck together and voted for it anyway.

Less than 24 hours after their surprising victory in the race for a vacant House seat, Democrats forced Senate Republicans on Wednesday to vote yes or no on a bill that would reshape Medicare, signaling their intent to use the issue as a blunt instrument against Republicans through the 2012 election.

Democrats staged the vote to press their advantage coming out of their victory on Tuesday in the contest, fought in large part over Medicare, for a House seat in upstate New York that had long been in Republican hands. Senator Harry Reid, the majority leader, brought the legislation to the floor so that Senate Republicans would either have to vote for it, exposing them to attacks from Democrats and their allies, or against it, exploiting growing Republican divisions on the issue.

No Democrats supported the measure, and five Republicans — Scott Brown, Susan Collins, Lisa Murkowski, Rand Paul, and Olympia Snowe — broke ranks to oppose the House plan. (Paul said it wasn’t ridiculous enough.) But 40 GOP senators voted to eliminate Medicare, while supporting the many other odious provisions in the House Republican agenda.

I guess I should give the GOP credit for chutzpah — this agenda is wildly unpopular, stood no chance of passing, threatens to cost the party dearly at the ballot box, invigorates their opponents, but the overwhelming majority of Republicans in both chambers just don’t care. Even after losing a special election the party should have won easily, the GOP just forges ahead with its right-wing vision.

Note, in particular, that some Senate Republicans who were thought to be less-extreme nevertheless went along with their party. Illinois’ Mark Kirk, who assured voters last year that he’s really a moderate, voted to support the far-right agenda that eliminates Medicare. Indiana’s Dick Lugar did, too, probably because he’s facing a more extreme primary opponent. Nevada’s Dean Heller, who voted for the House plan as a House member a few months ago, voted for it again yesterday as a senator, even though he’s running for a full term next year in a state with plenty of retirees.

I remember during the health care fight, when GOP lawmakers said sweeping proposals that the public hates must be killed immediately. To support such measures undermines American principles and flies in the face of “consent of the governed.” It looks like Republicans have changed their minds.

There were, by the way, other votes on alternate budget plans yesterday. The Obama budget was rejected unanimously — some said it cut too much, other said it cut too little — and the Toomey budget, which was basically the House version without Medicare cuts, failed on a 42-55 vote.

And then there was Rand Paul’s truly hysterical budget that, among other things, would have eliminated the Departments of Commerce, Education, Energy, and Housing & Urban Development. It failed on a 7-90 vote, with the Senate’s silliest members voting for it: Tom Coburn, Jim DeMint, Orrin Hatch, Mike Lee, Mitch McConnell, Rand Paul, and David Vitter.

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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.