Ok, I've had some time to think about the flip-flopper issue.  I am still concerned about someone who, at the age of 50, changes his positions on fundamental issues like life, campaign finance reform, etc.  I am even more suspicious when that person runs for president a few years later.

So why should conservatives be especially wary of flip-floppers? 

Precisely because conservatism isn't easy or popular.  If a person merely allies with the ideology of least resistance, it is likely he will eventually align with the liberal side ...