On one hand, I do see Klein's point. Candidates need to be salesmen, and that means they need to effectively market themselves to voters. Answers like:
"You know, I turned 50 last year, and I’m realizing I’m — if I’m not in the fourth quarter, I’m in the third quarter of the chronological clock."are not particularly energizing, and Klein makes the appropriate point that Pawlenty is going to have to do better than “because I’m getting older” and “I didn’t want to start taking it easy yet.”
On the other hand! Over at The Atlantic, I'm throughly sympathetic to Conor Friedersdorf's point that Pawlenty's answer is refreshingly normal. Politicians are people too, and sometimes they don't have the best answer for everything.
In the same way that romantic comedies shape our expectations about relationships in unrealistic ways -- "I knew from the first time I saw him that we'd spend our lives together" -- the conventions of presidential elections cause us to imagine that there should be some compelling narrative version of what brought someone into the race.
I'd like to place the correct answer somewhere in between the two. Candidates should be honest about the intentions and motivations of their candidacy, but that the same time need to offer voters a vision or platform to get behind.
The best answer Pawlenty (or any candidate) could have given, would have been something along the lines of "I can't give you the exact moment I decided that I wanted to run for the presidency, but I can tell you that my decision was ultimately cemented by the vision and leadership I can offer the American people."
Good salesmanship doesn't always equal dishonesty, but bad salesmanship does make your honesty harder to swallow.
UPDATE: I think Daniel Larison gets to the underlying point of Klein's Pawlenty critique:
Pawlenty’s candidacy doesn’t have any obvious rationale. In fact, the former Minnesota governor has trouble coming up with a reason why he is running at all. He doesn’t unnerve any major constituency in the party in the way that Huntsman does and Daniels did, but he isn’t that closely identified with any of them. He inspires neither intense loyalty nor especially strong dislike. (Bold mine - JG)It's not so much that Pawlenty's answer to Michael Crowley wasn't that compelling, but rather the rationale for Pawlenty's campaign as a whole is underwhelming. Klein's critique of Pawlenty's answer isn't valid on the answer itself, as it is on the overall motivations of his candidacy.