First, you have to actually have core convictions that naturally contrast with Hillary. Being pro-life, pro-family, pro-Constitution, pro-gun, etc, would go far.
. . . which naturally leads you to question the wisdom of nominating Guliani. Thompson isn't exactly my idea of a dream candidate (too close to McCain on CFR, for example), but unless Romney can make me believe, he's the closest thing we seem to have on offer. And here I admit that I do not seriously consider anyone below Huckabee in the polls. Any more than I consider that I should be the nominee - even though I agree with my own stands on the issues 100%.