One of them is a Republican senator and ally of the president. The other is a retired schoolteacher whom Republicans accuse of being a Democratic plant to siphon away votes.

President Trump told the Justice Department to intervene in the race, where polling shows Republicans at risk of losing a seat.

© Kerry Tasker/Reuters

No obvious legal authority supports a pre-emptive effort to block the certification of Alaska’s Senate election if the Republican incumbent narrowly loses.

© Kerry Tasker for The New York Times

The department, in a highly unusual lawsuit, argued that confusion over candidates with similar names could taint the election result.

© Doug Mills/The New York Times

The lawsuit centers on one of the president's longstanding complaints in the Senate race — the presence of a second candidate named Dan Sullivan who Republicans fear could siphon away votes from the incumbent in what's likely to be a photo-finish contest with Democrat Mary Peltola.