O'Malley was one of the first governors to endorse New York Sen. Hillary Clinton for president. Napolitano provided a key Obama endorsement just after his loss to Clinton in the New Hampshire primary. Napolitano has key homeland security credentials because of her experience with immigration as governor of a border state. O'Malley has key homeland security credentials because of his advocacy on the issue as Baltimore mayor.
There's no telling whether O'Malley would have been interested in leaving the State House for a federal post. But if Hillary Clinton had been on the stage today as president-elect instead of future secretary of state, might Maryland's governor have been standing next to her ready to take a seat in the cabinet?