In the case of this election, it's not clearcut I don't think, but fundamentally mobsters thrive better under a system where government lends them legal tools which they can rely on to push out competitors and carve a quasi-monopoly for themselves.

That's why they were heavily involved in and supported unionism and regulations of all kind which they could manipulate to crush competition, and those two tendencies are staples of the Democratic party and the left in general.