In The Spirit of the Laws, Montesquieu argued that a separation of the executive, legislative, and judicial powers of government is necessary to prevent abuses of power. He wrote that, if a single body holds all of these powers, that body can abuse it, but, if the powers are separated, each can check the other. He wrote that the legislative branch alone should have the ability to tax in order to prevent the executive from imposing its will arbitrarily. The president can veto acts of legislature, and the legislature is divided into two chambers that each check one another. The judiciary, Montesquieu thought, should be independent of the other two branches and should only concern itself with laws regarding threats to public order and security.*
An example of this is the Water Pollution Control Act Amendments of 1972 (aka, the “Clean Water Act”). This bill set a national goal of eliminating all pollutant discharges into US waters by 1985 while also making waters safe for fish, shellfish, wildlife and people by July 1, 1983. The bill passed the House by roll call vote 366-11 and the Senate by roll call vote 74-0 on October 4th 1972.* The Senate needs a simple majority of 51 votes to pass a bill while the House needs a simple majority of 218 votes to pass a bill.* So, the Clean Water Act easily passed both chambers of Congress.
President Nixon then had an opportunity to veto this bill. As the Constitution notes, every bill that passes the House and Senate must be signed by the president in order to become law. If the president returns it with objections to the originating chamber, it must be voted on again and receive two-thirds vote from both chambers before becoming law.*
In this case, President Nixon chose to exercise that Constitutional privilege and returned the bill back to Congress on October 17th. Nixon chose to do this shortly before midnight on that day which would have been 10 days from when he received it. If he had waited until after midnight, the bill would have automatically become law (another stipulation in the Constitution). On being returned to the House, not all members voted again. A two-thirds vote of the entire 435 body would be 290. Their vote of 247-23 means that only 62% of House members voted. However, of those who did vote, 91% voted to override the president’s veto. In the Senate, the breakdown was 52-12, again a large majority of a subset of the Senate. Thus, the bill became law on October 18, 1972.*