If the Senate ends up 50-50

[Skill and Chance]

What about Snowe?  Obama and company could make noise about negotiations with her in order to keep Lieberman in line if he threatened to switch.  She probably has even less to lose by switching, especially if LePage wins this fall.  

She could get Spectered, but that would be much less likely if she were the deciding vote for control of the chamber.  Of course you could also argue that she wouldn't get Castled if she was Republican #51, but Castle himself very well could have been Republican #51 this year...      

[Skill and Chance]

Come to think of it, a party switch might be a tantalizing choice for Mark Pryor, especially if Lincoln finishes under 40% next month.

[Skill and Chance]

Whoa, what? Specter was facing a loss in the general even if he got out of a primary (he wouldn't have). Snowe will cruise to victory. The establishment will do a lot more to keep a sitting Senator than they did for even Mike Castle. They had a chance to do this in 2006 and didn't despite the CfG targeting others. Collins hasn't been seriously challenged either and I see no reason for that to happen. It was clear Murkowski was in trouble after Daddy went down. Sitting Senator since 1994 gives you a certain stature that doesn't come with being simply an establishment supported candidate for Senate.

Not neccessarily from the vantage point of spring 2009. Back then it was very concievable that he would win re-election, and most Democratic insiders believed it. I'm not too sure about Snowe surviving based on the RINO hunt, and she is, of course, the most prominent "RINO." While I do not know many conservatives outside of LePage that would challenge her, people come out of the woodwork. But certainly, the establishment will see this one coming, and definitely will attempt to prop up Snowe. I am not a soothsayer. I just think that at this point, seeing "safe" candidates go down left and right, that it isn't hard to imagine Snowe being removed.

What "safe" candidates?

LePage wouldn't challenge her.

Democrats had a target on Specter for 2010 and he would've likely lost to a D if not an R. Well, he did lose to a D.

I could theoretically see LePage himself mounting a challenge.  It would be a lot more likely if he was further along in his tenure as Governor, though.  He could conceivably go after Collins in 2014,  but it would be surprising if the Tea Party has anywhere near today's clout by the time 2014 rolls around, especially if there's a GOP president.