It’s not true that he can’t run as a sitting governor. At a minimum, there is no question he can run as long as he submits an irrevocable resignation that would take effect on the day that he would take office as president if he were to win the election. (i.e. if he loses the presidential race, the resignation would still take effect)
However, that part of the law is murky, because it says that an “officer” of the state who submits such a resignation has to submit it to the Governor with a copy to the State Legislature, and that if a candidate who files for an election fails to submit the required resignation, the Department of State is to transmit that name as an automatic immediate notice of resignation to the Governor. So there’s some thought that it doesn’t apply to the governor since that would mean a governor is required to submit his resignation to himself or to receive notice from an executive branch agency that he has resigned.
At any rate, members of the legislature have already said they are probably going to change this law to allow him to run. Prior to 2018, there was no language that would have prevented it. The “Resign to Run” law that existed in 2018 had these exceptions:
o Candidates for federal office;
o Persons seeking the office of President or Vice President. (ss. 99.012(3)(a), (6), and (7), F.S.)
I’m not sure why they changed it, but I think they should change it back. I think it’s possible they changed it in anticipation of Gillum possibly winning the gubernatorial race in 2018, and then him being selected to run as someone’s VP candidate in 2020.