Mark McKinnon, the chief media consultant to McCain, wrote in a campaign memo last year that if Obama won the Democratic nomination, he would not actively campaign against him. With the results of Tuesday night's primaries in Kentucky and Oregon, Obama claimed he had a majority of convention delegates.

McKinnon said Tuesday evening he was making good on his pledge, and was "moving from middle linebacker to cheerleader" for McCain.

"I'll still be around from time to time in my lucky hat," McKinnon said in an e-mail, referring to his familiar black felt cowboy hat.

The former Democrat worked for President Bush's 2000 and 2004 campaigns. After signing on with McCain, McKinnon stayed on even as the Arizona senator's campaign faltered, losing staff and running out of money before climbing back to win the New Hampshire primary in January.