You are basically asking whether the federal government could prevent a state prosecuting an individual (1) because that individual's supporters would respond so violently or (2) because of concerns that Trump would lash out and spill the beans in prison?
I am not aware of such a provision and I can't imagine one existing (but I will research). The first concept would undermine the very concept of a government as it’s basically permitting mob rule: the latter is more interesting but would also basically allow the feds to block any state prosecution of an ex president or someone with similar security info. Also, constitutional red flags all over the place.
Off the top of my head state criminal prosecutions are enjoined where the state statute’s constitutionality is disputed: even then it seems there are (or at least have been) circumstances where being able to appear in court to raise the issue of unconstitutionality of the statue you are charged under is considered “enough” to permit the state case to go ahead.
I will however point you to this memo relating to the watergate affair which does mention that some of what you’ve mentioned could well be a factor in deciding whether to prosecute. Factors against prosecution were the following:
Points 3-5 are the most relevant to Trump’s circumstances/your question.
