I was reading an article in the New York Post by Dick Morris who came to this conclusion, made his case and i totally agree.
Morris believes that the only person that can beat her is Rice. Guiliani, McCain could but they wont get the nomination.
McCain is prolife so I guess you're hypothesis is wrong! Hillary would defeat Frist, Allen would defeat Hillary, and Santorum vs. Hillary would be a get out the base close election. We all know who wins those
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Like most people you're making a huge mistake by looking only to the Senate for the two major party candidates. While Hillary is the front-runner for the Dems right now. There are many governors who could make a run at her (Warner, Richardson). I predict that the 2k8 Republican nominee will be a governor as I don't see enough charisma out of the senators (save Allen) for any of them to garner the nomination.