I don’t know why you think the majority of the Senate would argue they have no jurisdiction with the current make up of the Senate. They most certainly will use Belknap as an ‘excuse’.
I never said that I do.
The Belknap case stands for the proposition that each house of Congress can do whatever the hell they want whenever they want. It is up to the courts (and ultimately to the states) to decide whether what they are doing is Constitutional. So far, no court has ever ruled on the issue.
The courts do not like to get involved in the inner workings of Congress, but that is not what is at issue here. This is the democrats trying to effectively pass an unconstitutional bill of attainder against President Trump based upon the pretext of punishing what was clearly constitutionally protected speech.