Spitzer vs Regulators

Eliott Spitzer has cut a wide swath across the US regulatory fabric. With the SEC and others asleep at the switch Spitzer has charged and convicted the high and mighty who have been stealing from the rest of us.
Lately the courts are saying that Spitzer overstepped his authority by chasing after banks who may be in violation of lending practices. My question is who is regulating the banks? Why does it take a state attorney general to do the heavy lifting.