What role is the President acting in when he vetoes a bill passed by both houses of Congress?

By threatening a veto, the President can persuade legislators to alter the content of the bill to be more acceptable to the President. Congress can override a veto by passing the act by a two-thirds vote in both the House and the Senate. (Usually an act is passed with a simple majority.)

Explanation:

the rebels’ chances of victory at lexington & concord were fairly slim, given the fact that most of them very untrained and they were up against the world's greatest military force.  

answer; genetics;