What is a congressional override of a presidential veto?
The idea of checks and balances comes to play in this issue. The house that originally passes the bill just needs a simple majority to have it go to the executive branch. If it is vetoed by the president, it is sent back to the house in which it originated. In order to override the veto, it is much more difficult for congress. They need to obtain a two thirds majority in each house for the veto to be overridden. Because in more cases than not, the bill did not pass with this high of a majority, it is very difficult for the veto to be overridden. Until recently the average override was 1 of every 18 vetoes. It has increased in later years to be 1 in every 5.
