The mistake was Juan McShame
The problem isn’t just McCain, it is the process by which we let the media and states like Iowa and New Hampshire determine WHO will be in the field of GOP candidates. Since Ohio and Florida are swing states, let them have more say in the early days of the election. Texas never gets an opportunity to vote for conservatives by the time the presidential primary gets around.
If it hadn’t been McCain in 2008, we probably would have had Romney, or Huckabee. No win situation there.
A mistake from which the GOP has learned exactly and precisely nothing.