Democrats' net gain of at least seven seats in the 2026 Senate elections secured their majority for the 120th Congress, establishing the party's internal leadership contest as the decisive factor in this market. Chuck Schumer enters that December caucus vote as the incumbent leader with stated support from most returning members, though some newly elected senators have signaled potential opposition. Traders assign Chris Van Hollen and Brian Schatz the next-highest probabilities as alternative Democratic choices, while Republican candidates remain near zero after their conference losses shifted them to minority status. The timeline runs through the caucus meetings and any subsequent floor vote, with Schumer's position strengthened by the scale of the Democratic victory.