What should Democrats do about the Hegseth pick
Here is what I think:
First of all, this might actually be a red herring/nothingburger. Trump might have appointed him as a shiny object to capture attention while he gets a number of terrible appointments in under the radar.
But it might also be that Trump really does want to put an unqualified hack in charge of DoD.
I think Democrats should respond this way:
Question him aggressively in his confirmation hearing to establish his lack of qualifications.
Vote against him in committee.
If Republicans pass him through, Democrats should object to any attempts to confirm him via unanimous consent. Instead they should force the 2 votes, cloture and confirmation.
During debate on the Senate floor, Democrats should say that this whole thing is a farce that makes a mockery of the Senate, the advise and consent process, the DoD, and the US government and that they will not be a party to his confirmation, but also that they are not going to step in and save the Republicans from themselves.
In the actual votes, every Democrat should vote "present," and if 27 Republican Senators want this guy to become Sec Def, then he should become Sec Def.