A simple majority in Congress can bring the nation to a halt. Congress can blackmail Bush.
If the President refuses to either sign or to veto a bill passed by both houses of the Regress, said bill becomes law in 10 days' time -- UNLESS the Regress have passed the bill within 10 days of the end of the Regressional session, in which case the President may ignore said bill (this is the so-called 'pocket veto').
If that latter condition is not met, the President must specifically veto said bill, or else it will become lawful statute by his failing to veto after 10 days.