What happened to those supporters?
McCain's main support came, not from Republicans, but from those "independent" darlings (aka democrats who are embarrassed of their party).
As for the pubbies who supported McCain, I think they were mostly made up of those who still nurse an unquenchable desire for a Republican who is popular with the media....McCain's love affair with the media would've lasted only until he started implementing pubbie policies.
Slight correction - McCain's media darlingship would have lasted only until he became the Republican nominee. They would have "sadly" found many reasons why Algore should win over McCain, and turned on a dime against him.