Reid Wilson reports for the WaPo:

Federal agents on Thursday arrested powerful New York Assembly Speaker Sheldon Silver (D) on federal corruption charges, stemming from payments he received from two New York City law firms.

Jennifer Queliz, a spokeswoman for the U.S. Attorney's office in the Southern District of New York, confirmed Silver was in custody Thursday morning. U.S. Attorney Preet Bharara will hold a press conference Thursday afternoon to announce the charges.

There is an interesting federalism question on the constitutional basis for federal prosecution of corrupt state officials.  It generally hinges on some tenuous connection with mail or interstate commerce.  In my view, a corrupt official denies the honest people of the state equal protection of the laws.  The bribe-payor gets special treatment that the honest people do not.  That is, of course, why he pays the bribe.  I haven't gotten any takers for my view yet.

Whatever the basis, prosecuting corrupt state officials is one of the most important functions of federal law enforcement.  Some valiant prosecutors do go after crooks who hold their purse strings, but we cannot expect that as a matter of course.