The best evidence I can give you (and I am not supporting Guiliani or anyone else) is that he has amassed a lot of support which is tied to his no-nonsense attitude with Arafat, the Saudi Prince, and crime-fighting.
I think his tough-guy image would inspire confidence in people (although that part is simply my opinion). On numerous occasions he has supported the President on the war without any of the waffling I have seen from Brownback and Romney.
The Iraq War is incredibly unpopular nationwide, and is the cause of Republican losses in 2006. Giuliani's support of it will hurt him in the general election.
He will never be President.