Stumping in South Carolina on Monday, John McCain unloaded on Donald Rumsfeld, calling him “one of the worst Secretaries of Defense in history.” Funny: I seem to remember that when Rumsfeld stepped down after the fall elections, McCain saluted his years of service.

Alas, this is a familiar pattern with McCain. In some ways he is one of the most admirable men in America. He seems consistent, fiercely independent, and principled. But at other times, he seems eerily reminiscent of Bill Clinton, constantly playing to reporters or to whatever audience he happens to be addressing.

It turns out that McCain is best when he is in dissent. That’s when all the indignation, the toughness, and the “straight talk” come through. His reputation, after all, has been made largely through breaking ranks with Republicans, a move that never fails to win applause from the press. On issues like campaign finance and the treatment of prisoners in the war on terror, McCain loves being at odds with the White House or Senate leaders. (Nebraska Senator Chuck Hagel, by the way, has studied McCain closely and does a plausible version of the GOP maverick, which is rapidly becoming a stock character on Sunday talk shows.)

Being a lonely voice of reason in a crowd is not a bad trait in politics. But it is an odd position for someone hoping to lead the GOP. Today the party is fractured and desperately in need of someone who will make the case for a post-Bush Republican vision. It is a task that demands a good deal more than merely distancing yourself from past party leaders.