There's some buzz today about David Ignatius' column in the Washington Post, the one in which he suggests that Barack Obama may be too tightly wound to win the Democratic presidential nomination.

"Obama is certainly charismatic, so much so that people often describe him as a rock star on the campaign trail," Ignatius writes. "But he's more Paul McCartney than Mick Jagger -- so cool and self-conscious that it's hard to imagine him saying, 'let it bleed.' He may be the smartest candidate in either party this year, and also the most visionary. But traveling with him, you get the sense that he's tight as a tick. He's Mr. Cool, holding himself back, wary of letting audiences see either his passion or his vulnerability."

Yeah, some people do describe Obama as a "rock star" on the campaign trail. People like, oh, say, David Ignatius.

Here's what Ignatius wrote about Obama just seven weeks ago:

"Obama has indisputable star power. Travel with him on the campaign trail and you see the high-voltage connection he can establish with people. When he walks through a hotel lobby or jumps out of his motorcade in shirtsleeves to greet an impromptu crowd, the persona is closer to a rock star than a typical politician. And for all the loose talk about whether Obama is 'black enough,' I saw many dozens of African Americans here crowd around him with obvious pride and passion."

The challenge for Obama, as Ignatius described it in August: Can he translate his "charisma" into a "serious political movement"? The challenge for Obama, as Ignatius describes it now: Can he loosen up enough to "ignite voters and win the Democratic nomination"?

Has Obama changed, or has Ignatius? We wouldn't presume to answer that question, but we will note this: The columnist's new theory turns heavily on two pieces of evidence -- the tone of Obama's book, "The Audacity of Hope," and the way in which the candidate delivered a speech in Iowa City. The book came out in 2006, and Obama delivered that Iowa City speech in May, three months before Ignatius wrote the first of his two columns.