John McCain has repeatedly been on both sides of a number of major issues, and to an extent has gotten away with it because the liberal media has been covering up for him.
However, it will be interesting to see what he tries to do on the Republican party platform at the convention.
If he tries to push his views on a number of critical issues, he's going to have a major fight on his hands.
Its not always the case that a candidate receives a "bounce" from the convention, just ask Michael Dukakis.
Here's a WaPo article link:
http://www.washingtonpost.com/wp-dyn/content/article/2008/07/06/AR2008070602322.html