No matter who emerges as the Democratic nominee, having McCain as the GOP standard-bearer seems to pretty much burst Michael Bloomberg's third-party bubble. (Haven't heard much on that front lately, have we?) On the other hand, it still leaves a fair amount of space open - relatively speaking, I mean - for Ron Paul to make a third-party run under the Libertarian banner. True, McCain isn't as ideal a foil for Paul as Rudy Giuliani would have been, but given his maximalist position on Iraq and his leftward tilt on immigration, one can certainly see the rationale for Paul to attempt a Nader-style protest candidacy - one that would also presumably attract a few Naderite votes from the anti-war left as well. I doubt he'll do it, but the opening is there.
Ross Douthat is a contributing editor at The Atlantic.