Well, look, here's what happened. You've got a company, AIG, which used to be just a regular, old insurance company. Then they insured a whole bunch of stuff and they were very profitable and it was a good, solid company.
 
Then they decided –- some smart person decided, let's put a hedge fund on top of the insurance company and let's sell these derivative products to banks all around the world –- which are basically guarantees or insurance policies on all these sub-prime mortgages.
 
And this smart person said, you know, none of these things are going to go bust; this sub-prime thing, it's a great deal, you can make a lot of profit. So they sold a whole bunch of them –- billions and billions of dollars. And what happened is, is that when people started going bust on sub-prime mortgages you had $30 worth of debt on every dollar worth of mortgage –- and the whole house of cards just started falling down.
 
So the problem with AIG was that it owed so much and was tangled up with so many banks and institutions that if you had allowed it to just liquidate, to go into bankruptcy, it could have brought the whole financial system down. So it was the right thing to do to intervene in AIG.

Not going to solve the political problem of the bonuses, but it's not a bad place to start...

Update: The Times says Obama has hinted at support for the bonus tax legislation:

In a statement, President Obama suggested he was supportive of the legislation, urging Congress to deliver a “final product that will serve as a strong signal to the executives who run these firms that such compensation will not be tolerated.”

But I didn't entirely get that impression from his Leno appearance:

Well, look, I understand Congress' frustrations, and they're responding to, I think, everybody's anger. But I think that the best way to handle this is to make sure that you've closed the door before the horse gets out of the barn. And what happened here was the money has already gone out and people are scrambling to try to find ways to get back at them.

--Noam Scheiber