Some libertarian friends are considering voting for Trump because they are deeply concerned about unified Democratic government in an era when progressives appear to be gaining influence. I agree with that concern, and with a normal Republican president I could approve of their vote. But Trump isn't normal.
I see one of two prospective outcomes of a second Trump term where he faces a unified Democratic Congress that intends to give them nothing.
In the first case, Trump retreats into a permanent sulk, accomplishing little, whining incessantly, claiming credit for a few things the Democratic Congress passes, and working around the edges here and there to get what he wants by following the practice well-established by his predecessord, including Obama, of claiming more presidential authority than he Constitutionality has. This would be tolerable, except for the very fact of his continued presence. Trump is fundamentally a weak man, so I think this is quite possible.
In the second case, Democratic obstruction of his goals, and particularly investigations of his businesses and conflicts of interest drive Trump into such a rage that he begins taking truly extraordinary measures to exercise power unilaterally, bypassing Congress wholly on policymaking, imposing his own budget, etc., and investigating and arresting political opponents (as he has recently called for).
I think outcome 1 is more likely. Trump is weak and has more bluster than strength. But outcome 2 has sufficient plausibility, and could be far more destructive than whatever progressive policies Democrats could actually manage to enact (less, I am confident, than the progressives are advocating), that I think the "stalemate" argument for voting for Trump is short-sighted and unwise.