Condition: Democrats control the U.S. Senate when the 120th Congress convenes on January 3, 2027: Democratic senators plus independents who caucus with them hold at least 51 seats (a 50–50 Senate is Republican control because the Vice President is a Republican). Otherwise this market resolves N/A.

Resolves YES if any justice of the U.S. Supreme Court retires, resigns, dies or otherwise leaves the Court between January 3, 2027 and January 3, 2029 (inclusive). A retirement counts when it takes effect; an announced retirement that has not taken effect by January 3, 2029 does not count. Resolves NO otherwise.

This is one half of a conditional pair; its twin asks the same question if Republicans keep the Senate. Comparing the two shows what the market thinks control of the Senate changes.

Starting probability is a seed, not a forecast: anchored on public prediction-market prices where a related market exists, otherwise a prior.