Ballots in the future will allow you to mark a first and second choice for president. When your first choice is out of the running, your vote will count toward your second choice.
Why is this important?
We need to have built in run-off elections so that voters can show their support for candidates who are not in the lead without feeling like they're "throwing away" their votes. This is important because it allows people to support a third party candidate, and it may be that the alternate candidate is the best choice.