LIKE LEMMINGS OFF A CLIFF…. House Republicans, after a very brief debate and a week of consideration, actually voted to pass Paul Ryan’s radical budget plan this afternoon. The final vote was 235 to 193. No Democrats voted for the measure, and despite some GOP anxiety going into the vote, only four Republicans had the nerve to vote against it. [Update: Here’s the roll call.]

The GOP leadership and Paul Ryan are no doubt pleased with themselves for pushing this extremist proposal through the House so quickly, with a largely unified caucus. As it turns out, perhaps the only people even happier with the outcome are House Democrats.

For anyone who takes these matters seriously, the Ryan plan is a radical mess. Its numbers don’t add up and it’s based on fraudulent expectations. It eliminates Medicare, guts Medicaid, slashes funding for key domestic priorities, and lavishes another massive tax break on millionaires and billionaires. The whole initiative is sold as a deficit reduction plan, but it doesn’t actually reduce the deficit — it just shrinks government and transfers wealth from the bottom up, imposing cruelty on elderly, disabled, and working families.

But nearly every single Republican in the chamber voted for it anyway. A year after running a campaign agenda that bashed Democrats for Medicare reductions, practically the entirety of the House GOP just voted to privatize Medicare out of existence.

Democrats can barely believe their good fortune.

Paul Begala noted the other day, “I hope every vulnerable Republican in Congress signs on to the Ryan plan to kill Medicare, because we will beat ’em like a bad piece of meat.” Non-partisan election analyst Charlie Cook thinks the plan may even put the GOP’s House majority in jeopardy.

And this morning, DCCC Chair Steve Israel (D-N.Y.) told Greg Sargent, “When we win back the majority, people will look back at this vote as a defining one that secured the majority for Democrats.”

The polling on this is unambiguous — Americans aren’t buying what Republicans are selling. Indeed, the GOP has it entirely backwards, killing programs the public wants expanded, cutting taxes the public wants raised.

Not only did 98% of the House Republican caucus agree to take the leap off this cliff, they did so knowing full well that this budget plan has absolutely no chance whatsoever of passing the Senate.

It’s likely Americans won’t watch today’s developments especially closely. There’s been very little national debate about this budget plan — it was only introduced last week — and the public doesn’t realize exactly what this agenda includes.

But it’s Democrats’ job to remind Americans about this remarkable vote every day for the next year and a half. By all indications, Dems are eager to do just that.

This was a test for the Republican Party. In 2011, is the party really that radical? Does it really have that few moderates left? Is the GOP really that far gone that extremism that was up until very recently considered beyond the pale can now enjoy overwhelming support in the party?

We received a loud-and-clear answer to these questions this afternoon. Voters will have their chance to offer an answer of their own a year from November.

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.