This afternoon, the House voted to pass Paul Ryan’s plan to end Medicare as we know it, a vote that DCCC chair Steve Israel predicted to me earlier today would be a defining one that would enable Dems to recapture the House.

That is an optimistic prediction, to be sure. But Chris Cillizza argues this afternoon that today’s vote could indeed create major problems for the GOP in 2012. And he gets at a key reason why — Nancy Pelosi’s success in keeping Dems united against the proposal:

Nancy Pelosi succeeded in keeping Democrats unanimously opposed to the budget, ensuring that when election season rolls around Republicans will own their budget vote fully.

It’s a tried and true strategy and one that was successfully employed by Senate Republicans on President Obama’s economic stimulus bill — only three Republicans voted for the plan — and the health care law that garnered zero GOP votes.

The lack of GOP involvement in those two pieces of legislation allowed Republicans to run — and run hard — against both proposals in the 2010 election.

Reverse the party names and substitute “budget” for “health care” and you get some sense of what some GOP incumbents might be headed for next fall.

Politico had a snide article the other day labeling Pelosi the “incredible shrinking woman,” arguing that “her diminished stature has affected the way she is percieved in Washington’s power game.” Yes, Pelosi does not have the power she once did. But we’re seeing here today that Pelosi can have an impact in unseen ways.

It’s also emerging that Pelosi is one of the key people who privately urged Obama to draw a hard rhetorical line on Medicare in his speech, precisely because House Dems want to campaign on it in 2012.

The other day, Pelosi suggested that Dems should model their campaign against the Ryan proposal on the Dems’ successful defeat of the GOP drive to privatize Social Security in 2005. Pelosi won that battle by insisting that Dems remained unified, and by ensuring that the contrast between the parties remained crystal clear. It remains to be seen how closely Dems will hew to that playbook this time, and there are differences between the two moments that may merit a somewhat different approach. But as Cillizza suggests, we may be seeing the first indications that Pelosi could end up having more of an impact on the larger political dynamic than one might have expected.