The two-party US system is not normally a problem of choosing between two candidates, because the multiple choice part happens in the primary.

In the general election you're reaffirming your support for your party's candidate as you've already made your choice. It's only the non-committed people mostly in the center who chose to only select from two candidates that have only two choices.

Of course this time the Democrat party failed to use a primary of many candidates to select their nominee.