Hillsborough County is the city of Tampa which has been ‘D’ controlled since the Great Depression. Its US House Seat has varied by number as Florida’s population has grown and Congressional Districts have been added and boundaries moved. But from post-Reconstruction to Kathy Castor ‘D’ today, Tampa has always had a ‘D’ Congress-critter.
For a Republican Presidential Candidate to challenge in Hillsborough makes the Democrats fear for the near-legendary I-4 Corridor that runs from Daytona to St Petersburg and has been indicative for many recent Presidential Race outcomes. FYI: In Clearwater which is north of St Petersburg in, neighbor-to-Hillsborough, Pinellas County, they set the (very temporary) Guinness Record Trump boat parade in August of 1.2k plus participants.
They might want to stop putting many eggs in the I-4 basket. That corridor has a huge sinkhole right in the middle of it. The Orlando area that once attracted Walt Disney, specifically Orange County, Osceola County (Kissimmee) and the now-deteriorating Seminole County have all gone (or are in the process of going, in the case of Seminole) hard left.
Republican candidates for President won metro Orlando every single time from 1948 to 2004. They are 0 for 3 since and the trend isn't a positive one.