Congress is responsible for legislation, but the president has to sign a bill before it becomes law and also has the option to reject, or veto, the bill. A presidential veto isn't necessarily the end of a bill though. If there is enough support for the bill, members of Congress can override the veto with a two-thirds majority vote. This is part of the checks and balances plan. The president can check Congress's power with a veto, but Congress can check the president back with an override.