It’s the fact that he’s:
-pro gay marriage
-supports government funded abortion, an assault on two facets of conservatism (fiscal and social)
-has no problem with using statist methods to achieve his goals
-is the quintessential opportunist (running on his 9/11 heroism and nothing else)
-makes most “big government conservatives” look like Tom Tancredo
-Has no inclination at all of securing the border
-Has a horribly chaotic family life
The fact that Giuliani does not respect the principles of the consitution should be a key issue for Republican primary voters.