the unwritten rule of senatorial courtesy applies to what appointments
Senatorial courtesy Senatorial courtesy is a long-standing unwritten, unofficial, and nonbinding political custom (or constitutional convention) in the United States describing the tendency of U.S. senators to support a Senate colleague in opposing the appointment to federal office of a presidential nominee from that Senator's state.[1] The practice is motivated by a general sense of collegiality among Senators and the assumption that a Senate colleague will have the best first-hand knowledge of the personal character and qualifications of nominees from his or her own state. It is also viewed as an "important source of political patronage"[2] for U.S. senators.
United States district court A judge of a United States district court is officially titled a "United States District Judge". Other federal judges, including circuit judges and Supreme Court Justices, can also sit in a district court upon assignment by the chief judge of the circuit or by the Chief Justice of the United States. The number of judges in each district court (and the structure of the judicial system generally) is set by Congress in the United States Code. The President appoints the federal judges for terms of good behavior (subject to the advice and consent of the Senate), so the nominees often share at least some of his or her convictions. In states represented by a senator of the President's party, the senator (or the more senior of them if both senators are of the president's party) has substantial input into the nominating process, and through a tradition known as senatorial courtesy can exercise an unofficial veto over a nominee unacceptable to the senator.