Paul Ryan’s endorsement of Mitt Romney has the potential to be important. Some Republicans have started throwing their weight behind Romney as part of an establishment push to expedite the end of the primary process. Others are backing Romney now to enter the vice presidential sweepstakes. While both of those could be factors here, the Ryan endorsement could go beyond that.

Ryan has been critical of aspects of Romney’s record, particularly Romneycare, in the past. But he’s noticeably warmed to Romney in recent months and it’s worth noting his argument that voting for Romney isn’t “settling”: “I was not a fan of Bob Dole being our nominee in ‘96, I didn’t support John McCain throughout the primary, I supported other people last time.This is not the same kind of candidate.”

Crucial here is that Ryan has calculated that Romney represents the best chance to get his fiscal blueprint, in the former of the budget that passed the House yesterday, signed into law. Romney has been supportive of the Ryan plan, including the broad outlines of what the House Budget Committee chairman would like to do to restructure Medicare. The current version of the Medicare plan in the House budget more closely resembles what Romney has specifically endorsed than last year’s budget.

Ryan could tie Romney to a comprehensive conservative agenda on entitlements and government spending, thus giving conservatives a stake in his election, in a way that the candidate has never been able to do himself. One factor that could mitigate that is that there has been more conservative criticism this time around, both in terms of wanting a budget that cuts spending faster and some of his Bush-era votes on issues like TARP. But some conservatives will be more inclined to vote for Romney if they believe he will play Ronald Reagan to Ryan’s Jack Kemp.