The rule is universal: neither a material witness to, nor a victim of, an alleged crime can serve on the jury before which the person accused of that crime is tried. There are good reasons for this, amongst them jurors are to be disinterested.
The Article of Impeachment, in relevant part, states: On January 6, incited by trump, members of the crowd he had addressed ... unlawfully breached and vandalized the Capitol, injured and ... menaced Members of Congress, the Vice President, and Congressional personnel...
Const. Art. I, sec. 3, cl. 6: “The Senate shall have the sole Power to try all Impeachments... [N]o Person shall be convicted without the Concurrence of two thirds of the Members present.” That does not say two thirds of the total Senate.
Two current members of the United States Senate were not present in the chamber on January 6 and thus would not be disqualified from sitting as jurors. The vote is based on “two thirds of the Members present.”
GOP Senators fear for their safety - or the safety of their seats. Several commentators say that, were the vote on impeachment by secret ballot, trump would be convicted in a second. Those Senators fear mobs the incitement of which gave rise to trump’s impeachment.
Senators have been sworn for the impeachment trial. That status should be reconsidered. In any Court of law, all but two of the Senators would be disqualified for cause. To allow a trial to continue in such circumstances would be considered fundamental error.
If ours is a system based on the Rule of Law, we should adhere to basic rules of law across the board. Jurors should be able to cast their votes without fear of reprisal by the thugs they are impaneled to try.