The voting system used by the US, called "plurality voting", is notoriously flawed. Voters who favor a third-party candidate are forced into a dilemma: they can either vote sincerely and "waste" their vote on a third party, or vote defensively and pick the lesser of two evils.
Plurality voting suppresses new ideas and encourages campaigns built around negative attacks. The effect of this system is to virtually exclude all but two political parties (The last third-party president was elected in 1850).
The solution is well known and deceptively simple: rewrite our ballots to use a fair system such as "instant runoff voting". This voting system is used in several US cities and worldwide with great success [see, for example, fairvote.org/what-is-irv].