For those missed the first few minutes of the debate, an early question from Jeanne Cummings went to Barack Obama: Why, she wanted to know, was his plan superior to hers if estimates suggest that 15 million people would remain uninsured?

Readers of this space have heard about this debate aplenty.  Most of those who care to form an opinion on it have; those who don't have moved on.  And that's just fine.  Personally, I'd be happy to say nothing more about it.

But I've just received a press release from the Obama campaign suggesting that 15 million figure isn't reliable.  It cites articles noting that Clinton got her figure from a New Republic piece I wrote some time ago -- which is, according to one of the "factcheck" articles cited, "hardly an authoritative source."

So just to clear the record, let me restate what I stated in my follow-up articles on this subject: 

The estimate was based initially on an interview with Jonathan Gruber, the MIT economist whom all the campaigns (including Obama's) consulted for estimates of how their plans would work.  It was a rough estimate, as these estimates usually are, but as reliable as any of the other numbers that get thrown around in campaigns

Subsequent to that, I interviewed several other economists. The consensus was that Gruber's estimate was pretty good -- and that, more important, the basic underlying point was right: Without a mandate, some significant portion of people would remain without insurance. The only dispute was how big a difference it would make.

Not everybody agrees; Robert Reich, among others, has said he thinks the argument is hogwash. But based on my discussions with people who actually study health care policy -- i.e., the real experts on this -- I believe it's correct.

Those two follow-up articles about the debate are  here and here.

But let me just add one more thing. Just yesterday, the Urban Institute released a report on this issue.  I had consulted some of their scholars in my initial round of interviews.  Since that time, they've done more formal estimates.  Their new estimate is that a plan like Obama's would leave... 15 million uninsured.  (Actually, 15.5 million.)

Here's the money quote from that report:

Opponents of an individual mandate argue that they can come close to universal coverage with a combination of income-related subsidies, more options for purchasing affordable coverage (e.g., through purchasing pools), and administrative mechanisms for facilitating enrollment in insurance. The most recent data indicate that there are 47 million uninsured people in the United States. Even if subsidies, benefits, and administrative simplifications are sufficient to reach two-thirds of the uninsured (a reach beyond what any study to date has shown for a voluntary system), this would still leave 15.5 million people uninsured.This would be admirable, but would be considerably less than full coverage, and, as health care costs and insurance premiums increase, these numbers could easily erode unless further government dollars were injected into the system.

Just to be totally clear on this, I think the distinction here is an important one -- as much for what it says about the candidates' thinking as for the actual policy details. Among other things, I tend to think -- as Clinton has argued -- that you are more likely to achieve something approaching full universal coverage if you start out with a rhetorical commitment that everybody will be covered.  To me, it's a matter of pushing the debate as far as possible -- and mandates do that.

I also think Clinton deserves credit for bravery.  If anybody is the one telling "hard truths" here, it's her. 

But now we're moving into strategic calculations about which, frankly, reasonable people can have a lot of disagreement.  And whatever you think about mandates, that doesn't mean Obama wouldn't do great things for health care reform. 

As Obama himself noted -- and as I wrote earlier this week -- Ted Kennedy, who has arguably done more to advance the cause of health care reform than anybody in Washington, believes Obama can deliver universal coverage.  That means something.

What's more, Obama's promise to push legislation through with a combination of public pressure and brokering deals with hostile special interests is consistent with the way he operated in Illinois -- where, as I reported not long ago, he really did impress a lot of health care reformers with his savvy and dedication to the cause.

Perhaps most important, the most critical element in passing universal health care will be the number of Democrats in Congress.  If Obama has longer coattails -- if he can really build a larger Democratic majority, as many of his supporters claim -- then that's a definite vote in his favor. 

So Obama has great potential as a health care reformer.  (Indeed, overall I thought he sounded far more crisp and self-assured in this debate than I'd heard before.)

But about the policy question asked during the debate -- whether this mandates make a difference -- the overwhelming consensus among experts is that they do. 

--Jonathan Cohn