Why no bail out for Lehman Brothers?

Why was the Bush Administration willing to bail out Bear Stearns, and take over Fannie and Freddie, but drew the line at bailing out Lehman Brothers? How's this for a reason:

Investment bank Lehman Brothers Holdings Inc., which filed for bankruptcy-court protection early Monday, has been the eighth-largest corporate giver to Sen. Obama's campaign this election cycle, with Lehman employees donating $361,000. Source

And what do you want to bet AIG doesn't get federal help either:

Trouble at several other companies could hurt fund raising for Sen. Obama and other Democrats. Employees of insurance giant American International Group Inc., for example, have given 66% of their $647,000 in total political donations to Democrats in the current election cycle, after favoring Republicans from the mid-1990s through early 2000s. (same source)

AIG -- too big to fail, I guess.