1. Successful executive experience (in either government or private industry).
2. A decent track record when it comes to supporting conservative issues (someone who compromises on certain issues for political reasons is acceptable, but one who does this on 23 out of 25 issues will never be able to credibly stand up and call himself a "conservative."
3. Any executive experience in government must have been in a traditionally conservative jurisdiction.
Item #3 basically disqualifies almost any candidate from the Northeast, Illinois, and the West Coast. That may sound like a silly criterion for someone to have, but I will never trust a candidate who has run a successful campaign in a city or state that would rightly be called a Communist enclave in any other era.
You're a couple of centuries too early.
In the future, they might be able to take some Reagan DNA, some Giuliani, some Bush, (anyone want some Buchanan too) etc, mix then up in a test tube, and clone a candidate to run a couple of years later.
But in this day and age it is easy to disparage a successful performer like Giuliani in comparison to the perfect phantom.