MoveOn has put together a Bush-McCain Challenge to clarify just how close the two are.  You can take the challenge yourself here.  Here's a little of their text:

It's hard to tell the difference between George W. Bush and John McCain. Here are resources where you can get the facts:
ThinkProgress - The Real McCain - McCain Source

Here are sources for all the questions in The Bush-McCain Challenge:

1. Q: Who promised that U.S. troops would be greeted as “liberators” in Iraq?
   

   A: McCain. (Dick Cheney said that, too. In fact, McCain is more of a Bush-Cheney hybrid. Which is a pretty scary thought.)

   Source: "But I believe, Katie, that the Iraqi people will greet us as liberators." --John McCain, NBC's "Today Show," March 20, 2003
   "I think things have gotten so bad inside Iraq, from the standpoint of the Iraqi people, my belief is we will, in fact, be greeted as liberators." --Dick Cheney, NBC's “Meet the Press,” March 16, 2003

2. Q: Who went on a nationwide speaking tour trying to convince Americans to privatize our Social Security? .....

Take the challenge yourself and learn more. And there are lots more illuminating questions (and answers, with documentation) online, here.