The blue slip is a paper form — literally blue — that the Senate Judiciary Committee has sent to home-state senators since 1917 when the president nominates a judge for a federal court in their state. A senator can return it favorably, return it negatively, or withhold it entirely. Historically, a withheld or negative blue slip could block a nominee from receiving a committee hearing. The tradition is not codified in Senate rules — it is a committee courtesy that the chair can honor or ignore. Its practical force depends entirely on who chairs the Judiciary Committee and their willingness to respect the tradition. Republicans weakened it for circuit court nominees during the Trump first term; the Biden era saw continued inconsistency.