McCain is a maverick. It remains to be seen if Bush can feel secure and serene with McCain bouncing around the playing field. Presidents like to have their vice presidents shut up for long stretches. And Al Gore's seven long and lean years of apprenticeship under Clinton cemented him in the role of Clinton's understudy. Bush also has to think long and hard about what happens if a Bush-McCain ticket loses to the Democrats.
Presidential nominees look at running mates with a whole new set of spectacles.
The classic cases of nominees taking bitter foes onto the ticket are JFK and Reagan. Kennedy embraced Lyndon Johnson after being persuaded he needed the Southerner to balance the ticket sufficient to win the Electoral College. But in a Detroit hotel room on the eve of the 1980 convention, Reagan was persuaded that only by embracing Bush, the candidate of the Eastern Establishment and the Non-Voodoo School of Economix, could he dump an incumbent president. So there's ample precedent for taking a former enemy on as your co-pilot, if that's what it takes to win. Bush has alternatives.