Notice how your reply has nothing to do with justifying the conflation of "obstruction of Congress" with the actual crime of "obstruction of justice".
Notice that your reading comprehension skills are not even up to your grammar, which sucks.
Roberts has no Constitutional authority in the trial other than keeping order
The actual Constitution does not say "keeping order".
It's the role his mentor and predecessor in the same role embraced in the Clinton impeachment trial. Learn some history.
That was a trial, conducted somewhat as trials are - it had potential (at least) witnesses and evidence and so forth, for starters. Rehnquist did not have to deal with somebody like McConnell trying to pull stunts like excluding witnesses and evidence (deposition or live).
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Style guides do not follow traditional grammar rules, and they're often bastardizations of those rules. Exactly the sort of thing I'd expect you to cite.
So you didn't read it.
You fools don't even fact check when you're getting your noses rubbed in it.
The Chicago Manual does - famously, explicitly, to the point of being mocked, and including specifically and explicitly the example I provided you - follow traditional grammar rules whenever possible. The standard, traditional formulation of the possessive in that situation is exactly what it recommends, for exactly that reason - it's traditional, time-honored, standard, unambiguous, and familiar to every literate speaker of English.
The Chicago even - as is traditional - allows some slack in the system, for semi-literates such as you and for those with reasoned objections in certain special cases. It will "accept" certain variants, if the author is consistent. The example at hand - the formation of the possessive of "Roberts", a polysyllabic name in which the final letter sounds as an 's' rather than a 'z' - is not one of them. (One problem it would create involves the possessive of the plural - more than one Robert in possession. That plural possessive is formed thus: "Roberts' ". You see the issue - your illiteracy creates an ambiguity where there was none.)
If you don't like style manuals, for some reason or simply from apparent ignorance of them, there are always sources such as Garner's "A Dictionary of Modern American Usage" - same info, in a less pedantic context. Excellent book, btw - recommended.