As I’ve been noting here, one of the interesting things about the battle over the Paul Ryan budget — and the larger vision it represents — is that both sides are acting as if they’re utterly convinced it plays in their favor. While Dems are salivating at using the architect of the GOP plan to end Medicare as we know it to drag Mitt Romney down, the likely GOP nominee has only intensified his embrace of the GOP budget chairman.

Why is Romney doing this? Noam Scheiber offers an intriguing explanation: Romney has no choice. Romney, like John McCain and Bob Dole, has suspect conservative credentials, and both previous GOP nominees were dogged in the general election by suspicions on the right:

Romney, if anything, suffers even more acutely from this problem. McCain and Dole were war heroes, at least, which counts for something in conservative circles. They also hailed from conservative states. In the eyes of right-wingers, Romney’s résumé offers nothing remotely as redeeming. No surprise, then, that having effectively bagged the nomination, a time when you’d expect him to lunge for the middle, Romney is moving rightward.

How else to explain his strange embrace of Paul Ryan and Ryan’s Medicare-gutting, upper-income-tax-refunding budget in recent days? Given that the country is pretty down on Republicans, Romney’s only hope of winning the presidency is to distance himself from the party. And yet, over the last week, he’s done nothing but tie himself to the GOP’s most polarizing elements. He spent five days as Ryan’s wingman in Wisconsin and then explicitly defended the Ryan plan in Washington on Wednesday.

Were Romney remotely confident of his right-wing résumé, he wouldn’t be auditioning Ryan for vice president, as he appears to be, but dismissing him as a cold-hearted pipsqueak.

It has been widely assumed that Romney will at some point have to achieve separation from Ryan and the unpopular House GOP, in order to avoid alienating swing constituencies. But if Scheiber is right, this may not be an option.

Recall that many on the right saw the Etch-A-Sketch tale as confirmation that Romney will inevitably ditch the conservative positions he mouthed to get through the primary. They will be watching for any signs of deviation from those positions in the general.

Of course, it’s also possible that Romney is embracing Ryan because he agrees with his vision. While Romney really doesn't seem to see social issues as worth going to war over, he seems to genuinely hold views that are as radical as Ryan’s when it comes to the distribution of wealth, the role of government and the safety net, the priorities that should dictate how we fix our fiscal mess, and the cure-all powers of an unfettered free market. Or maybe Romney is convinced Ryan is a political winner even among swing voters. Maybe he thinks they will reward Republicans for claiming to be willing to tackle the deficit and entitlements, and won’t pay close attention to niggling details such as who would get stuck with the bill under their plans.

Whatever the reason, it does look like Romney isn’t letting go of Ryan anytime soon.