Rich, …I’m a conservative Republican, and I would be in favor of Lieberman as McCain’s VP pick (from a pragmatic standpoint). But I think that your point that Lieberman would have to pledge not to run for president in 4 or 8 years is not actually necessary. Being a semi-liberal “Democrat”, I don’t think Republicans would have any pre-conceptions of him as the default front-runner in a future primary. Bush (father), although not a conservative, started from the pole position in 1988. But Lieberman is just too far afield to have any similar advantage. He may or may not be in good standing with Republican voters in the future, but in either case that does not translate into frontrunner status in his case.
The only Lieberman “threat” is that he succeeds McCain before McCain’s term is up. That’s a calculated risk I am willing to take in exchange for higher probability of winning this November.