One day after Senate Republicans invoked a conduct rule to end Sen. Elizabeth Warren’s speech against the nomination of Sen. Jeff Sessions as attorney general, a 1986 letter from Coretta Scott King urging the Senate to reject Sessions’ nomination as a federal judge is gaining new prominence. Warren was reading aloud from the letter by King, the widow of Dr. Martin Luther King, when she was interrupted by the presiding chair of the Senate, who warned her of breaking Rule 19 , which forbids members from imputing to a colleague “any conduct or motive unworthy or unbecoming a Senator.”