I spend a lot of time participating in mock Congress's and U.S. governments and recently a question came up regarding the constitutionality of Senate rules that prohibit a Senator from making disparaging remarks against another Senator (e.g. calling someone an idiot or claiming that they're incompetent). In real life, rule 19.2 of the Senate reads >
No senator in debate shall, directly or indirectly, by any form of words impute to another Senator or to other Senators any conduct or motive unworthy or unbecoming a Senator.
I found that this rule was invoked by the Senate presiding officer when Elizabeth Warren called a Senator a "disgrace" during a confirmation session and was prohibited from speaking for the rest that session.
So, are rules like these constitutional? Do they infringe upon a Senator's First Amendment rights? I know that the Constitution clearly lays out that "Each House may determine the Rules of its Proceedings, punish its Members for disorderly Behaviour". Based on this, it seems obvious to me that the Constitution does not protect disorderly behaviour (and speech) by a Senator and it would make sense that the First Amendment does not extend to it. Is this correct and is there more nuance to this matter? How could I construct a cohesive legal argument to protect a rule like this? Thanks!