Rule XIX of the US Senate says: “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.” In effect, a senator may attack another senator’s position but not another senator’s motives. The wording was adopted in 1902, after two senators fought on the Senate floor.
On February 7, 2017, Senator Elizabeth Warren read from a 1986 letter by Coretta Scott King opposing Jeff Sessions’s nomination as a federal judge. Majority Leader Mitch McConnell said she had “impugned the motives and conduct of our colleague from Alabama.” The Senate voted 49 to 43, along party lines, to uphold the ruling against her. McConnell said: “She was warned. She was given an explanation. Nevertheless, she persisted.”