All legislation passed by both houses of Congress must be presented to the President. This presentation is in the President's capacity as Head of State.
If the President approves of the legislation, he signs it (sign into law). If he does not approve, he must return the bill, unsigned, within ten days, excluding Sundays, to the house of the United States Congress in which it originated, while the Congress is in session. The President is constitutionally required to state his objections to the legislation in writing, and the Congress is constitutionally required to consider them, and to reconsider the legislation. This action, in effect, is a veto.
A "veto" is used to prevent a law from becoming fully enacted.
veto
veto
The president can choose to veto a law.
Pocket veto
its not a law and will not a law
Congress cannot veto a law. Any law must be written and passed by Congress in the first place. The president can then veto it. Congress can override the veto with a 2/3 majority. After a law is passed, the Supreme Court can strike it down if they declare the law unconstitutional.
To strike down a law means that a court has ruled that the law is unconstitutional or invalid, and therefore unenforceable. This can happen if the law violates rights or principles guaranteed by a country's constitution.
His power of the veto, and the power he wields at the (supposed) head of his political party.
veto
the president
Sign it, veto it, do a pocket veto.