Well, we now have the first 2008 poll (PDF) showing John McCain losing Arizona to Rudy Giuliani. It’s from Behavioral Research Center, and shows Giuliani up a slim 2 points (definitely margin of error) over the Arizona senator in the Grand Canyon State. The results:

Giuliani: 20%
McCain: 18%
Romney: 11%
Thompson: 10%

Also: Polls, including one from Behavioral Research Center, have shown that McCain would lose a 2010 Senate reelection bid were Governor Napolitano to run against the great Maverick hope.