I take E.J. Dionne's predominant point about electoral prudence -- in fact we have all taken it, since Thomas Dewey -- but on this one minor-est of premises within a minor premise (which I have duly italicized) I dissent:
Democrats have an interest in the Republican contest going on indefinitely. Romney victories in Tuesday’s Michigan and Arizona primaries would likely shorten the process, and ending the nomination battle quickly is the precondition for a Republican counteroffensive.
What evidence exists that Romney victories tomorrow would in any way shorten the GOP's primary process? I don't see it.
Doubtless, two more Romney wins would contribute immensely to Romney's inevitability, but such inevitability has so far failed to impress or persuade a very substantial portion of a quite disgruntled GOP base. Yes, he da man; but they don't have to be happy about it, and of that, they've made no secret. And just because Romney may walk off with Michigan and Arizona tomorrow, as he's already done with New Hampshire and Nevada and Florida, there's little reason to think the base will suddenly be wild about Willard.
Both Gingrich and Santorum can live off the land (and a couple of billionaires) till June; which is to say, for us they can make life a delightful hell for Mitt Romney. In time, the base may have to swallow the former governor, but till then, they don't have to savor him. Thus enter the would-be spoilers, whose permanent doom Romney must continue to heavily invest in -- because one never knows.
And, if I may ... I still believe Newt Gingrich is "the story," more so than Rick Santorum. The latter was merely the last to be elevated to national notoriety, and like all the others -- Bachmann, Cain, etc. -- he'll fade, assuming he doesn't stupendously dynamite himself first. The base will remain in need of a Romney-alternative, though. So then comes a recycling process. And who's first in line? Who, that is, will be left?