The presidents power to veto an act of congress is an example of

It is an example of checks and balances.

Explanation:

US constitution is unique because the three offices of American government have been given a certain constitutional powers to work distinctly without becoming authoritative.  

Each branch of the government is stipulated with certain roles and responsibilities which cannot be overcome as each branch is authorized to exert supervisory and regulatory authority over the other so that no office becomes independent while exerting powers. Each office of the government is limited in their powers and all three offices are vested with equal powers  

explanation: we can only guess at how our actions may be perceived in the future. doing something really big like killing lots of people, saving lots of people, affecting the lives of lots of people is a sure fire way of being remembered in historical records. we can also make a difference in the history records by being a small influence on something bigger, whether that is as a civil servant, scientist or artist.

of course you could argue that we all affect history just as tiny cogs in a   bigger machine.

if you mean how do people influence our opinions of things which have already happened, then simply by writing a book which looks at things form a different perspective and trying to convince people that this perspective is more accurate or truthful. people do it all the time i.e. richard the third was a terrible or was he? plenty would disagree, it's just that their views aren't the most widely known.n:

a case involving the laws of a single state.