It’s been nearly 70 years since there last was a presidential election rematch, but it has occurred more than people might think in U.S. history.

Dissatisfied Democratic primary voters in Michigan have cast enough protest votes to deny President Joe Biden two of the state’s 117 delegates.

As the Republican presidential primary intensifies this summer, most White House hopefuls are devoting their time to events in Iowa and New Hampshire, the states that will kick off the nomination process early next year.

Many people in Florida opted in for early voting, possibly to skip the long lines on primary day or for a whole slew of other reasons. But what are you supposed to do if you voted early for a candidate who has already dropped out -- before Florida’s primary on March 17? And anyone who votes for that person will have his or her vote count -- as in, a vote for that candidate. Many states follow this same rule, but there are a few places that will let you have a re-do if your candidate dropped out before the primary. As you can see from this primary alone, many candidates drop out right before or directly after the juggernaut primary day.

Even if one candidate has more delegates than the other, that’s only a “plurality,” not a majority, per party rules. Candidates who earned delegates, but have since dropped out of the race, can try to push their delegates onto another candidate. A candidate needs to earn 2,375 delegates on subsequent ballots to win the nomination. However, having a contested convention is something the Democratic National Committee will do its best to avoid in the coming months. The last time a contested convention occurred was in 1952.