Gate News reports that on March 13, Polymarket prediction market data shows the probability of the Democratic Party sweeping the 2026 midterm elections rising to 46%, a record high. Since the outbreak of the US-Iran conflict on February 28, the Democratic sweep probability has surged from 5%. In comparison, the Republican sweep probability is currently only 17%.
According to Polymarket rules, if a party wins the majority of voting seats in the House of Representatives, that party is considered to control the House; if a party holds more than half of the voting seats in the Senate, or half of the seats with the Vice President (who has the deciding vote) belonging to that party, then that party is considered to control the Senate. Controlling both the House and Senate is considered a “sweep.” The US midterm elections do not include the president or vice president but elect Congress and some state governors, serving as a “referendum” or “barometer” on the current president and their party’s performance.