Kerry
Lieberman
Edwards
Biden?
Plus of course, the stealth candidate, Hillary.
This doesn't even count Rat senators who want to leave town to speak at universities, think-tanks, and media events. Those guys are stuck for the duration, because the ones who will get to leave will be the candidates. This should also cause the Rat candidates to be even nastier with each other.
And if they turn down an invitation, they will have to say why.
Devious plan. I like the way you think.