As far as the purcahse of the bad loans(MBS)

the congress did not how how much they are going to pay for $1. If they pay too much, the tax payers will lose money. If they pay too little, it will not solve the bank's liquidity problem.

And the real problem is no one knows the quality of those security except the lenders(sellers know, but the buyer don't know).

So, someone suggested the "Reserse Auction": So there is only one buyer(the Treasury) with so many sellers(banks).
And let the sellers bid the lowest price for those securities.

Still they have to figure a way to do it.