That was the early assessment of SCOTUSblog's Tom Goldstein, during a break in today's Obamacare oral argument. For one thing, Justice Kennedy -- the presumptive swing vote -- seemed genuinely concerned about the mandate's impact on individual liberty. On top of that, says Goldstein, Paul Clement -- the lead attorney for the challengers -- gave a "superb" presentation. I would add that Goldstein speaks as a friend of Obamacare -- literally. He wrote one of the amicus briefs supporting the mandate.
The argument is now finished, and the early buzz is that Obama has locked up (as expected) the votes of the four liberal justices, but it is not clear whether they can get a fifth vote. Kennedy may yet support the mandate; it's conceivable that Alito might as well. But, if they don't, Obama might come to regret scolding the Supreme Court on national TV for a decision (Citizens United) written by Kennedy with Alito concurring.
I'll post more once I've read the transcript.