Can an American president retroactively veto a law?

Then, once a law is a law, only another act of Congress, Constitutional Amendment, or judicial nullifcation (if the courts find the law is unconstitutional) can repeal it. The President, according to the Constitution, has no power to repeal a law on the books. read more

The president of the United States has he right to veto any bill sent to him by the Congress. If each chamber then votes 2/3 in favor of overriding the veto, the bill becomes law. The president also has the option to “Pocket Veto”, wherein the president simply doesn't respond to the bill and the congress goes on recess within 10 days of the bill being sent to the president. read more

A veto message is an explanation as to why the president vetoed the proposal. There is a second way that a president can veto a proposal called a pocket veto. Say a president refuses to sign a bill but doesn't reject it outright, and Congress adjourns, or takes a break, from its law-making cycle. read more