They're doing completely typical Twitter shitposting, on Mike Gravel's verified account. It's a funny joke, but that's all it is. You could hand over the account to anyone on lefty irony Twitter and get the exact same results.

It's been somewhat disheartening to see people take this at all seriously, to think that Mike Gravel is going to even have anything useful to say at the debates. We all (well, maybe not the teens) remember Gravel from 2008. He's not about to blow anyone's mind.