John McCain looked great on "Letterman" Wednesday night, as relaxed and charming as any politician can be when they are on their game.

McCain's charisma is an asset, but is it enough to revive his flagging presidential campaign?

In this era of media saturation, it is very difficult to rebrand a known quantity. It is as tough for Ford and Chrysler as it is for Britney Spears to be different from that which they have become in the public's collective mind.

The same is true of Sen. McCain. He has a blazing personality, but that's only part of the brand. The other parts? McCain-Feingold, the Gang of 14, McCain-Kennedy, Lindsey Graham.

I discuss the McCain brand at length in my new book, "A Mormon in the White House?" and conclude that while Sen. McCain is a great American, he's been a lousy senator and a terrible Republican. That's the brand.

Lots of products have mixed brands. I think of the Jaguar of the '70s — beautiful to watch, wonderful to drive, a nightmare to own. In politics, there's Bill Clinton, a gift to journalists in search of copy.

The McCain brand can't be saved by charm. Mayor Giuliani and Gov. Romney are both relatively new to most Americans, and they are both gifted with as much or more of the kind of energy that John McCain threw off in 2000. The rest of the GOP field simply doesn't have that energy, and the money totals will underscore that fact when the first numbers are published at month's end.

Pastor Phil is a friend of mine with whom I have an annual lunch when he vacations in California. His church is in Iowa, and earlier this year he accepted an invitation to meet Mitt Romney. He's never been one of the "I can't vote for a Mormon" evangelicals, but he is very pro-life and very serious about politics and government.

He was deeply impressed by Romney, and especially by his energy and intelligence. Serious people know just how extraordinarily difficult the world has become and will remain for America. To read even a little about our enemies is to be alarmed. To read deeply is to be certain that the next president must be both a skilled executive, a gifted communicator, and crucially, an optimist in Reagan's mold.

The mayor and the governor both have these skill sets, but McCain no longer conveys that last crucial aspect. His charm and charisma is of a different sort, and it doesn't appear to be the sort the Republican primary voters want. Continued...