A recent Cato podcast with Robert Levy explains why the Wall Street bailout is unconstitutional:
What is the intelligible principle underlying this bailout? There is none. “Making things better” is not an intelligible principle. And yet that is all that Congress has said to Henry Paulson. We are now having daily hearings trying to extract from Henry Paulson what it is he is going to do. After all, why hasn’t Congress told him what he is to do? He is the official to implement the laws of Congress, not to tell Congress what he is about to undertake.