Start with having the IRS auditing the banks for possible violation for REMICs. 

The main problem with Wall Street isn’t that, as Bernie Sanders says, the banks are too big to fail. It is that the bankers who run them are too big to nail—to be held financially and personally liable for the bad or corrupt decisions they make. This is now, sadly, documented history. The heart of the subprime mortgage mania—the real reason it could go on for so many years, nearly sinking the world economy in the end—was that no one was really held responsible for any of his or her bad decisions. Ever.

Bank executives weren’t held responsible during the bubble as it was building, when banks stopped caring about their own mortgage lending…