Consider the following sequence of events: Congress passes a bill. The president vetoes it. Congress overrides the veto. The bill becomes a law. What constitutional principle is at work? (CS 15)

The constitutional principle of separation of powers

Explanation:

A veto by the President simply means he excises his constitutional power to reject a bill passed by Congress.

However Congress can override the veto if approved by two thirds of the House, then the bill can become Law. This is done to prevent the President from blocking a bill when there is much support for it.