Florida is a Closed Primary state, which means that for a voter to choose the party nominee for a political party in a Partisan Elected race, the voter must be a registered voter of that political party to participate.
There are however opportunities for voters not registered as a Democrat or a Republican to vote.
They may vote in all Non-Partisan (at least in name) or no party affiliated races which under the Florida Constitution includes All Municipal City Council & Commission Races, County School Board Members (Presently) and almost all Judicial races from retention of Supreme Court members, Circuit and District Courts, County Judges and races like Soil and Water Conservation Board, Mosquito Control, Fire Districts, and Community Development Districts.
In rare instances, a scenario will come to fruition where all candidates that qualify in a partisan election are of ONE political party and no other candidates qualify that would appear on a ballot in the general election from another major political party or a write in candidate.
In this scenario, a Universal Primary Contest occurs. When all candidates for an office have the same party affiliation and the winner will have no opposition in the general election, all voters, regardless of party affiliation, will have the opportunity to vote in this race.
In Manatee and Sarasota County, this has happened and in Senate District #20, Senator Jim Boyd will face opposition from John Houman and in Senate District #22, Senator Joe Gruters will face Michael Johnson.
In each of these races, the winner of the August 23 Universal Primary will win election and be sworn in to office for the new Senate Term.