Obama is the one who imposed what we might deem -- in appropriately Maoist parlance -- the Three Authoritarianisms. They were the Paris climate accord, the Iran deal, and US intelligence agencies being used to surveil American citizens.
All three of these authoritarianisms were entirely ex-Constitutional. The first two were in essence treaties on which Congress (and by extension the American people) never got to vote or, for that matter, discuss in any serious way. The Paris accord probably would have failed. As for the Iran deal, we still don't know the full contents and therefore debating it is somewhat moot. We have, however, seen its consequences -- corpses littered all across Syria, not to mention untold millions of refugees.
But what of his fourth--and in my view far worst--authoritarianism? Specifically the weaponization of the IRS? That nobody has been held accountable for this outrage is the greatest scandalous legacy of the late, unlamented administration.
Make it 5. Include the weaponization of the DOJ.