A controversy is nonjusticiable where there is "a textually demonstrable constitutional commitment of the issue to a coordinate political department; or a lack of judicially discoverable and manageable standards for resolving it . . . ." Baker v. Carr, 369 U. S. 186, 217.
In this case:
1. There is no texturally demonstrable commitment to the Senate of the right to try private citizens who do not hold any office from which they can be removed. Rather, there is an express Constitutional prohibition against bills of attainder (i.e., an act of Congress declaring a person guilty of some crime and punishing him).
2. There is a clear judicially discoverable and manageable standard for resolving it. Impeachment of an office holder is the only exception to the Constitutional prohibition against bills of attainder. Congress cannot declare that any private citizen is guilty of some crime and then punish him under the pretext of an impeachment trial of someone who is not then the holder of any office from which he can be removed.
2. There is a clear judicially discoverable and manageable standard for resolving it.
There is no judicial review of any impeachment proceeding. There is no judicial role whatsoever. See my #227.