Something that I find pretty astonishing is going to happen today in the House of Representatives: Republican members are going to hold hands and take a big leap into the unknown by putting their names — and votes — behind the Paul Ryan budget. I can’t think of a similar vote in recent decades — one that involved such a major change of policy on an issue people care about — that had so little a chance of being enacted into law and that had so little justification from the previous campaign.

Of course, Republicans ran on plenty of rhetoric about cutting government. But this is different; now, they’re really going to put themselves on the line in favor of a major transformation of Medicare. Indeed, they’re about to vote in favor of retaining the very Medicare cuts they campaigned against last fall. And they’re doing this even though few Republicans ran by touting a major overhaul of Medicare (there’s nothing about that, for example, in the GOP “Pledge to America”).

Not only that, but they’re about to take this vote with little realistic expectation that their Medicare plan will be enacted into law — unlike, say, the expectations of Democrats who supported health-care reform in 2009. Or, to take some examples from budget debates, these proposals are much less likely to be enacted than were similarly major changes supported by Democrats in 1993 and Republicans and some Democrats in 1981. It’s even less likely to be enacted than the Newt Gingrich budget of 1995. Certainly, it’s realistic for House Republicans to expect that the eventual 2012 budget deal will contain spending cuts, but as far as I can see, Ryan’s Medicare changes are highly unlikely to get through but quite likely to be a campaign liability for Republicans in November 2012.

Whether they’re taking this vote because of electoral courage, or because of electoral fecklessness in the face of the possibility of Tea Party primaries, or perhaps because they don’t realize what they’re doing . . . whatever the reason, this is big news.