While then Sen. Barack Obama was considering running for president, his advisor and friend David Axelrod worried in 2006 that Obama would have to toughen up for a White House campaign. Axelrod told Obama that he was thin skinned and he wondered if Obama could take the punches that would come in a presidential campagin.

"You care far too much what is written and said about you. You don't relish combat when it becomes personal and nasty. When the largely irrelevant Alan Keyes attacked you, you flinched," Axelrod wrote in a memo.

Axelrod's strategy memo to Obama is revealed in "The Battle for America 2008," a new book by Dan Balz and Haynes Johnson about the 2008 presidential campaigns.

Obama's charmed political career came in part because of puffy, fluffy non-critical press coverage. Axelrod fretted about how Obama would do in the rough and tumble of a campaign.

'It goes to your willingness and ability to put up with something you have never experienced on a sustained basis: criticism. At the risk of triggering the very reaction that concerns me, I don't know if you are Muhammad Ali or Floyd Patterson when it comes to taking a punch.'"