John McCain mentioned several times during his endorsement by George Bush that he would be campaiging with Bush to the extent that Bush's "busy schedule" allowed.
Take a look at Bush's schedule for October 2004, the height of the last general election campaign season. Multiple election events in multiple states, every day. September was nearly as busy.
This was the period when Iraq was descending into the abyss. If ever he would have a busy schedule, that was it. So what is the Straight Talking MaverickTM afraid of?