[Terr_]

> a Senate rule and the Senate sets is own rules via simple majority.

Right, each house of the US legislature starts the session with a >50% vote to re-adopt a slowly mutating package of rules that it used last time and has carried forward for decades, defining how work is scheduled, what committees exist, how seniority is calculated, who gets the nice office with the window, etc.

This leads to the "nuclear option" of a special >50% vote to remove the underlying rule which imposes the larger vote-margin for certain situations.