Why did McCain pick the governor of Alaska instead of the governor of South Carolina? Sarah Palin may well be generating more instant buzz than Mark Sanford would have. But much of it is negative, as people discuss whether someone who has been governor of a very small state for less than two years is ready to be a heartbeat away from making national security decisions. Even the devout conservative Ramesh Ponnuru of National Review can’t avert his eyes from the problem: “Palin has been governor for about two minutes. Thanks to McCain’s decision, Palin could be commander-in-chief next year. That may strike people as a reckless choice; it strikes me that way. And McCain’s age raised the stakes on this issue.”

Mark Sanford was a congressman for six years, where he served on the International Relations Committee as well as the Joint Economic Committee. Palin has been governor of 670,000 people for about 18 months, while Sanford has served for five and a half years as governor of a state with 4.3 million people. Like Palin, Sanford is a social and economic conservative. He has taken on the Republican establishment in his state government and has a strong record on both school choice and pork-barrel spending. He has four children and a modern political wife who worked on Wall Street for six years and has managed his campaigns.

So what advantage does Palin bring to the McCain campaign that Sanford wouldn’t? Well, she’s a woman. Pure identity politics, the sort of thing Republicans deplore but often practice.

Bill Kristol says that the difference between Palin and Obama is that the Democrats are running an inexperienced guy for president, while the inexperienced Republican would only be vice president. A fair point. But as McCain himself has said, his age guarantees greater scrutiny of whether his vice presidential candidate is, as the saying goes, “ready on day one to lead.” (When I Googled that phrase, Google asked me if I meant “ready one day one to lead.” Maybe she will be, one day.)

McCain likes to talk about his 95-year-old mother. But his father died at 70 and his grandfather at 61, so his age is a real concern.

Mark Sanford would have been an experienced executive who has already dealt with national and international issues and a great next leader of the Republican party. Sarah Palin? We’ll see.