Answer: Congressional leaders believe they have the votes necessary to override a veto.
All legislation passed by both houses of Congress must be presented to the President. If the President approves the legislation, then he signs it into law. When the President chooses not to sign, he must return the bill to the house of Congress in which it originated. This action is a veto. However, if the Congress overrides the veto by a two-thirds vote in each house, it becomes law without the President's signature. Therefore, it is more common for the Congress to pass a bill the President has threatened to veto if the Congressional leaders believe they have the necessary votes to override it.