The Trump administration sued Alaska and state election officials Thursday over the candidacy of Dan J. Sullivan, arguing that his name could confuse voters and affect the outcome of the state's U.S. Senate race between Republican incumbent Dan S. Sullivan and Democratic challenger Mary Peltola.

The lawsuit, filed by the Justice Department and the U.S. Attorney’s Office for the District of Alaska, asks a federal judge to prevent the state from certifying results potentially affected by voter confusion until officials can investigate whether ballots cast for Dan J. Sullivan were intended for the incumbent.

Federal attorneys argue that the two candidates’ similar names could divert votes from the sitting senator and potentially change the outcome of a closely contested race. Alaska uses ranked-choice voting in its general election, and the candidates are distinguished on the ballot by their middle initials.

Dan J. Sullivan, a retired teacher and former U.S. Forest Service worker from Petersburg, Alaska, entered the race as a Republican before being listed on the ballot without a party affiliation. State election officials initially attempted to remove him, arguing that his candidacy could mislead voters, but Alaska courts ruled that he could remain on the ballot.

Dan J. Sullivan has denied that he is running to confuse voters or help Peltola. He has said his candidacy reflects his dissatisfaction with the incumbent senator and his desire for political change.

President Donald Trump criticized the challenger Wednesday, calling his candidacy a “SCAM” and promising legal action. The administration filed its lawsuit the following day.

The case could have significant implications for a Senate contest that may help determine which party controls the chamber after the November midterm elections.