The final leg of the legislative journey is the White House, where the president can either sign the bill into law or veto it. (You can learn more about the veto power in Chapter 9.) But even if the president rejects the legislation, Congress still has one final recourse — it can override the president's veto with a two-thirds vote of both chambers. This process, however, is extremely difficult and rare, so much so that less than 5 percent of all presidential vetoes have been overridden. In fact, Congress had been in existence for fifty-three years before it successfully overrode its first veto, overturning President John Tyler's rejection of a tariff bill.

In 1996, the Senate fell nine votes short (after the House had surpassed the two-thirds threshold) of overturning President Clinton's veto of a bill that would have banned third-trimester abortions, one of the most contentious override battles in recent times. Nevertheless, the ability to override a veto remains one of Congress's most important checks over the presidency.