Wasn't George Mitchell originally Edmund S. Muskie's Senate successor? He was also a federal judge. And popular with the Bushes too
What makes you think he was popular with the Bushes?
He made GHWB's Presidency a partisan hell. Another poster says GW as Rangers' owner cast the dissenting vote to keep him from being Baseball Commissioner. I didn't remember that myself, but the poster was saying GW did that as payback for Mitchell's unrelenting partisanship against his dad. Also, a different poster has a quote from Mitchell totally badmouthing the Iraq War and saying the result is we must start withdrawing.
The Bushes are generally polite and personable, but I don't see how George Mitchell fits into their scene as President Bush's U.N. Ambassador.