John McCain’s top adviser complains that the media apply a double standard when they cover his candidate. “They think they’re on the level with McCain, that he’s not the old McCain,” Mark Salter tells The Atlantic, “but he is the old McCain. He just doesn’t know what happened to the old press corps.”

Let me explain.

For the longest time, I was sitting on the fence, as were many centrists. A former Hillary Clinton supporter, I was bothered by Barack Obama’s thin résumé, his rock-star rallies and the sexism tolerated by his campaign. At the same time, I admired McCain for his fiscal rectitude, history of bipartisanship and concern over global warming. That the right wing despised him for several high-profile breaks with the Bush administration – notably on torture and the early tax cuts – was a plus.

In June, I ran some interference for McCain among Hillary voters: I shared my genuine belief that despite his “pro-life” voting record, McCain probably wouldn’t take steps toward outlawing abortion – and if he did, the Democratic House and Senate would stop him. I gave some pretty good evidence (though I forgot to mention McCain’s vote confirming Justice Ruth Bader Ginsburg, the most pro-choice member of the Supreme Court).

My thesis that McCain had shown some latitude on the issue was roundly slammed in both The Nation and The New Republic. The Nation wrongly implied that I hated Obama. (Not loving isn’t the same as hating.) The New Republic item was better reasoned but oddly ignored a recent interview in which McCain said that he would consider a pro-choice running mate, namely former Pennsylvania Gov. and ex-U.S. Homeland Security Secretary Tom Ridge.

Suffice it to say, I wasn’t always in the tank for Obama. Nor was the public, which, polls showed, stood evenly divided into early September.

What happened, Mark? Sarah Palin happened.

Independents like me wanted two things out of a McCain running mate. (1) A capable leader who could step into the top job should something happen to the not-very-young No. 1. (2) Someone who would temper McCain’s recent efforts to woo social conservatives. They got neither in the Alaska governor.

Sure, Palin gave him a bump in the polls right after the Republican convention. She gave a rousing speech, written by a crack speechwriter. But once on her own, she quickly displayed a shocking ignorance of world affairs and a general inability to talk coherently on policy matters. Her habit of dividing America – even individual states – into good and not-as-good sectors comes off as downright weird.

Just look at the RealClearPolitics poll averages dating back to early September. The McCain-Palin numbers started cratering about a week after the convention, which was two weeks before the stock market did.

Independents tend to be fiscally conservative, socially liberal and strong on defense. They were McCain’s natural constituency and in mid-September gave him a 13-point margin. That lead has since flipped over to Obama, and Palin is a big reason. The choice of her as McCain’s VP would have been politically brilliant had a Democrat made it.

As recently as three months ago, partisan Democrats were accusing centrist pundits of giving McCain a free pass by ignoring his conservative record. Maybe there’s still an old John McCain under what we now see. But who can tell?

Obama also deserves much credit for the change in attitude. He dropped the rock-star persona and showed himself to be an informed and disciplined candidate.

The new Obama might have won over the fence sitters under any scenario, but one thing is obvious: If McCain had named Ridge as his running mate, he’d be getting a whole lot more love right now.