Sloppy Seconds
From Ryan Lizza's Campaign Journal at The New Republic:

The cable networks have given lots of coverage to the new Bush ad, "First Choice," which shows McCain praising the president, an effort to remind voters that McCain rejected Kerry's appeals to join the ticket. But I haven't seen any mention of the fact that in 2000 Bush asked McCain if he was interested in being his running mate, and Bush was similarly rejected. I had completely forgotten about this bit of history until several people today e-mailed me this quote from McCain on "The Today Show" on March 18:

"I'm not running for vice president. President Bush in 2000 asked me if I was interested in being vice president. I said no then. I'm not interested in being vice president now."

Sounds like Cheney was Bush's second choice.