A federal appeals court sided with Republicans seeking to use district boundaries redrawn last year to give the G.O.P. an advantage in the upcoming midterms. The Supreme Court has twice cleared a path for Missouri to hold its general election under an older map that would likely help Democrats retain both of their congressional seats in the state.

The messy legal battle over Missouri’s congressional map returned late Tuesday to the Supreme Court for a third time this month. Ballots reflecting those voting lines were mailed to overseas and military voters last week, but a decision Monday night from the U.S. Court of Appeals for the Eighth Circuit reopened questions about the map.

The state’s primary was held in August using the redrawn, pro-Republican map, meaning many voters would be choosing among general election candidates whom they had no role in nominating. Proponents of the older map asked the Supreme Court on Tuesday night to block the appeals court order. The justices asked for a response from Republican congressional candidates by 2 p.m. on Wednesday.

Missouri was among the states that redrew congressional maps outside the usual once-a-decade cycle at President Trump’s request. Republicans currently hold six of Missouri’s eight U.S. House seats, and the new map could help determine control of Congress.

Secretary of State Denny Hoskins said redistricting was not eligible for a referendum, but the Missouri Supreme Court disagreed and ordered the question to appear on the November ballot.

Credit: David A. Lieb/Associated Press