The Constitution authorizes the Federal government to guarantee a republican form of government in the states, and that is the only authority it has over their internal decisions. This includes the state's sovereign rights to regulate murder within the state. Whatever you can say about Florida's government, it is a republican form of government.
The 14th amendment forbids any state from enforcing any law which abridges the privileges or immunities of citizens of the United States. But then “state’s rights” confrederates aren’t big fans of the 14th amendment are they!?