And at the University of Oklahoma, students involved in filming and posting a video showing a woman applying blackface were expelled this week.

Mr. Ertel, 49, had been the supervisor of elections for Seminole County since February 2005 when Mr. DeSantis, a Republican, appointed him secretary of state in December. Before resigning, he had testified before a state legislative committee on Thursday about election lawsuits.

A few days after President Trump was inaugurated, Mr. Ertel publicly disputed Mr. Trump’s claims of rampant voter fraud.

“To be clear: voter fraud is likely one of the least-committed felonies in America,” he wrote on Twitter, using an account that has since been deactivated. “Barring system-wide collusion, it is simply not the case that ‘millions voted illegally.’”

But Mr. Ertel also acknowledged that there were flaws in the system that could be manipulated, and that he was committed to “non-arduous provisions” that would allow the most citizens to cast their vote.

As part of his duties as secretary of state, Mr. Ertel was in charge of the state’s effort to restore voting rights to 1.4 million ex-felons, which Florida voters approved in November.

He had received many awards for his work on increasing voter registration, including the Martin Luther King Jr. Good Citizenship Award given by the city of Longwood in Seminole County.