National Public Radio had a succinct look at last weeks' squabble over health care between Democratic frontrunner Sen. Hillary Clinton and her closest rival, Senator Barack Obama. The Clinton campaign is taking Obama to task for claiming that his health plan will cover everyone even though the plan has no mandate for individuals to buy insurance.

It seems like a trivial distinction between plans that are so similar (and similar as well to the proposals put forward by Sen. John Edwards and New Mexico Governor Bill Richardson) that without the obligatory "Paid for by'¦" at the bottom of the fact sheet you'd be hard-pressed to say which campaign issued which proposal. In all of them, people with insurance can keep their plans, and those without can buy into federal plans, with subsidies to those who can't afford it. (See my discussion of Clinton's plan here and Richardson's plan here. Slate's Timothy Noah has elegantly dissected offerings from both Obama and Edwards.) Yet the Clinton campaign is undaunted. "It is impossible," Clinton says, "to get to universal health care if you don't have a mandate."

The Obama campaign retorts that a mandate won't do much good either unless it comes with enforcement mechanisms -- something that neither Clinton nor Edwards offered to detail until, as NPR's Julie Rovner points out, criticized by Obama. In recent days both Clinton and Edwards have floated ideas like automatic enrollment and garnishing wages. Among the pundits, the New York Times' Paul Krugman has come out behind Clinton, while Noah backs Obama, on the grounds that if all the plans are, as Noah maintains, gradually introducing socialized medicine, there's no point in antagonizing a large bloc of voters with a mandate.

So who's right? I put the question to Henry Aaron, a senior fellow at the Brookings Institution, and got pretty much the answer I expected: it doesn't matter. "The big difference is between the Democrats and the Republicans," he said. "All of the Democrats have made it crystal clear that they intend to make major changes" to the health care system. But "if you want to get picky about it," he added, Obama's right. "I don't think an individual mandate will get you universal coverage."

You might think, then, that the power of persuasion (or intimidation) in even an unenforced mandate would at least get us closer to universal coverage. But Aaron is skeptical about that for another, more fundamental reason. Whoever occupies the White House in 2009 will have to submit their health plan to a Congressional thrashing. The Obama and Clinton health plans might be (slightly) different now, but they would end up exactly the same.