The source is impeccable: Mark Salter, McCain’s chief speechwriter, on the record.

[L]ess than a day before he was set to speak in New Hampshire on April 25 [of last year], McCain ordered his aides to excise the paragraphs describing the pledge.

“Lots of ideas get raised with the candidate. He made a decision and we didn’t do it,” Salter said in a brief telephone interview this afternoon. He said that “no speech is final until the candidate signs off.”…

Campaign advisers said that, as they discussed the merits of the pledge, the drawbacks were obvious: it might tie McCain’s hand with Congress. It would certainly raise the profile of his heir apparent and vice presidential nominee, who would be treated as a de-facto presidential candidate for McCain’s entire term. And it would draw attention to his age.

But at the time, the benefits were judged to be equally as powerful: his finance team loved it; it would call more attention to the political opportunism of his opponents, Republicans and Democrats. It would free him from having to spend the last two years of his presidency running for re-election; it would send an unmistakable message that McCain intended to be a different kind of president. One Republican close to the campaign said: “It would have been the most selfless act in modern American politics.”

Yeah, and the fact that millions of voters are now going to hear that he wouldn’t go through with it will leave the impression that he’s not so different or selfless after all. He made the right decision for the reasons Ambinder gives, particularly given that he’ll be facing a deep blue Congress that would have every incentive to gridlock him if they knew he was on the clock, and admittedly it’s not like Obama’s in a position to taunt him on this, but why on earth would the campaign confirm it? I don’t get it. Exit question: Any possibility of the pledge returning later this summer as a buzzworthy stunt if Maverick starts to fall too far behind? The only way he’d do it is if his VP pick was exceedingly popular. Hmmmm.