Mocking the President is only fine when its a Republican in the White House, when a commie is in the White House the commies in the Entertainment Industry say nothing, because they all voted for him
Unless you're Jay Leno. He was liberal but that did not stop him from making jokes about Bill Clinton.
The last Democrat President SNL mocked was Bill Clinton, I remember a pretty funny sketch where Phil Hartman (RIP) as Clinton was in a McDonald's for a meet and greet. Taking customers food while campaigning and he tells a Secret Service agent "there's a lot of things we wont be telling Mrs. Clinton."
They took some shots at Al Gore before and after the 2000 election. Particularly portraying Gore and G.W. Bush as Felix Unger and Oscar Madison in an Odd Couple parody where they share the White House.
Once Mr. Obama came into office, they refused to mock him and effectively worshiped him and Mrs. Clinton. Biden is a target rich environment for parody, but you wont see it on SNL.