What he said:
With respect to health care, I’m actually — continue to be confident that the Supreme Court will uphold the law. And the reason is because, in accordance with precedent out there, it’s constitutional. That’s not just my opinion, by the way; that’s the opinion of legal experts across the ideological spectrum, including two very conservative appellate court justices that said this wasn’t even a close case. [How many of those expert thought so after the Supreme Court argument?] . . .
And I think it’s important, and I think the American people understand, and the I think the justices should understand, that in the absence of an individual mandate, you cannot have a mechanism to ensure that people with preexisting conditions can actually get health care. [Why should the justices care about a policy argument? Obama is confused as to their “mandate” — to interpret the Constitution] So there’s not only an economic element to this, and a legal element to this, but there’s a human element to this. And I hope that’s not forgotten in this political debate.
Ultimately, I’m confident that the Supreme Court will not take what would be an unprecedented, extraordinary step of overturning a law [courts strike down unconstitutional laws all the time] that was passed by a strong majority of a democratically elected Congress [it barely got by the House and had no room to spare in a party-line vote in the Senate]. And I’d just remind conservative commentators that for years what we’ve heard is, the biggest problem on the bench was judicial activism or a lack of judicial restraint — that an unelected group of people would somehow overturn a duly constituted and passed law. [Obama and the rest of the liberal legal establishment has been saying the opposite for decades] Well, this is a good example. And I’m pretty confident that this Court will recognize that and not take that step.
How the President clarified his comments:
The point I was making is that the Supreme Court is the final say on our Constitution and our laws, and all of us have to respect it, but it's precisely because of that extraordinary power that the Court has traditionally exercised significant restraint and deference to our duly elected legislature, our Congress. And so the burden is on those who would overturn a law like this. Now, as I said, I expect the Supreme Court actually to recognize that and to abide by well-established precedence out there. I have enormous confidence that in looking at this law, not only is it constitutional, but that the Court is going to exercise its jurisprudence carefully because of the profound power that our Supreme Court has.
(The clarifying remarks also brought Lochner into the picture, and Volokh Conspiracy's David Bernstein pounces.)