McCain has a history of personal friendship with the opposition. His loyalty to Morris Udall was legendary. McCain would visit Mo daily in the hospital after Mo was stricken with Parkinson's. It did not alter his voting pattern.
McCain is co-chair of Bush's campaign in Arizona. As senior Senator he is titular head of the Arizona Republican Party. To defect and run with a New England liberal would guarantee an Bush win in Arizona.
McCain would lose influence if he ran with Kerry and won. He would lose even more if he ran with Kerry and lost.
Why would he join with the party that just trashed his crowning achievement, CFR?
If Kerry/McCain won it would leave no line of succession in the Democratic Party and with that, no future.
How many votes would a pro-life, free trading maverick at the bottom of the ticket bring to the Democrats when the alternative is a pro-life, free trading Bush is at the top of the other ticket. How many Democrats would stay home?
However, promotion of McCain by the Times, Peters and Kristol for VP (or SecDef) acknowledges two verities: The Dems know Kerry is weak and therefore vulnerable on defense issues and want to improve his credentials though his campaign thinks defense (Vietnam service) is his strongest suit. Second, The Dems know that McCain can do serious damage to Bush's prospects for reelection, especially for his sway with independents.
But McCain would be foolish to take the nod since it would mean giving up his chairmanship of the Senate Commerce Committee where he can rail against pork, his pet peeve. Also he would be relinquishing his role as a media darling, which was gained by being a maverick who often sides with Dems and never hesitates to criticize Bush. Dems love how he undercut the GOP on campaign finance reform while rarely criticizing 527 circumventions by the Dems.