Ahh, my favorite named fallacy. The fallacy of equivocation.
Ziggurat says "be impartial". The oath says "do impartial justice". SB (and many, many, others) say they mean the same thing.
It's weird. One senator can say, "I am not impartial", and there are howls of "OATHBREAKER!". Meanwhile, three senators who happen to want to be the next president can publicly declare that Donald Trump should be removed from office, and there are a few such shouts, but when you listen carefully, it seems that the shouting is coming from a different corner. No one who condemns one is condemning the other.
Before anyone says something stupid about "whataboutism", let me head this off at the pass. "Whataboutism" is jargon that occurs when one side says that a certain behavior is ok because the other side is as bad or worse. That is absolutely, unequivocally, NOT, what I'm doing.
I'm saying that neither side is doing anything bad here. The requirement to "do impartial justice", doesn't mean that no senator can have an opinion, or that no senator can express that opinion publicly. It means that each of us, with a special emphasis on senators, needs to judge the case according to its merits, not according to polticial considerations.
Have you all done that? Well I would hope that you at least did your best, and yet, it seems that both public opinion and senators' statements are strongly divided along party lines. So it often is. It's human nature. And yet, each will say that party affiliation has no influence on their judgment.
I, for one, cannot look at either side and say the people on side A have made a fair and impartial judgment based on the facts and/or the law, while the other side is a bunch of partisan hacks who are simply interested in the political consequences of the outcome. To me, both sides seem pretty political in this.