The department filed suit late Thursday in federal court in Alaska, asking that the state not certify results potentially affected by voter confusion while the government investigates. The case centers on Republican Sen. Dan Sullivan and Daniel J. Sullivan Jr., a retired schoolteacher from Petersburg who is also running for the seat.

Appearing Sunday on CNN’s “State of the Union,” Blanche denied that the lawsuit was intended to give President Donald Trump a way to challenge an unfavorable election result. “President Trump is not trying to take over a state election in any way, shape, or form,” Blanche said. Trump, however, told reporters Friday that he had directed the department to file the case: “I’m the one that said do it.”

The Justice Department cited the National Voter Registration Act and argued that the similar names could confuse voters. Blanche characterized the requested relief as preventing certification if Alaska’s law has been broken, leaving the dispute to the state and its courts. The department has not explained how it could determine whether ballots marked for Daniel J. Sullivan were intended for the senator, given that ballots are secret.

Alaska election officials distinguish the candidates on the ballot: the incumbent appears as “Dan S. Sullivan,” with a Republican label, while “Daniel J. Sullivan Jr.” appears without a party label. The state’s ranked-choice system also allows voters to rank both candidates. In the August primary, the senator received more than 68,000 votes, compared with 4,107 for the other Sullivan.

Alaska courts, including the state Supreme Court, previously rejected efforts by Republican election officials to remove Daniel J. Sullivan from the ballot. Those officials argued his candidacy was intended to mislead voters; he has said he chose to run himself and denied seeking to confuse voters or draw support from the incumbent.

Sen. Lisa Murkowski, Alaska’s other Republican senator, has backed her colleague’s reelection but criticized the federal lawsuit, saying the state had already distinguished the candidates. Democrats have also argued the case risks interfering with the electoral process. The Senate contest is viewed as important to Republicans’ effort to retain control of the chamber.

In the CNN interview, Blanche pushed back sharply when anchor Dana Bash raised his earlier reference to a “doomsday” scenario involving federal intervention in certification and asked whether the case echoed events after the 2020 election and the Jan. 6 Capitol attack. Blanche called that comparison “crazy.”

The lawsuit puts a federal challenge to Alaska’s election procedures into a high-stakes race shortly before voters cast ballots. The dispute now turns on whether the Justice Department can establish that federal law requires action despite state courts’ decisions to keep both candidates on the ballot.