Even billionaires hurt when they spend maybe $200 million dollars and have nothing to show for it. No mafia tactics imagined by Trump are needed. They fought a battle to stop Trump that drained their budgets for the primaries and have zero to show for it.
It begs the question though, why would Trump even make the threat? Either he doesn't have evidence and just want to silence opposition, or he has evidence and will proceed. But if he has the evidence, why not just release it and destroy the corruption for good? I would suggest that the point is not to eliminate the corruption, but rather to control it.