The Trump administration filed a federal lawsuit on Friday seeking to block the certification of Alaska’s Senate election if the Republican incumbent, Senator Dan S. Sullivan, narrowly loses. The legal action, lodged in federal court in Alaska, focuses on concerns about voter confusion caused by the presence of another candidate on the ballot with a similar name: Daniel J. Sullivan Jr., also a Republican.

President Donald Trump confirmed that he personally directed the Justice Department to pursue the case, highlighting the administration’s increasing involvement in election-related legal disputes. The lawsuit contends that the similarity between the candidates' names could mislead voters and potentially affect the outcome of the election against Mary Peltola, the Democratic challenger who is currently polling closely with Senator Sullivan.

Alaska’s ballot includes four candidates, among them Daniel J. Sullivan Jr., a retired teacher from Petersburg who recently registered as a Republican despite previously voting for Democrats, including Peltola. Republicans have argued that this second Sullivan is a Democratic plant intended to siphon votes from the incumbent. However, Alaska’s Supreme Court previously ruled in June that Daniel J. Sullivan Jr. could remain on the ballot.

David Becker of the Center for Election Innovation & Research described the Justice Department’s move as unprecedented and potentially politically motivated. “DoJ making this claim this late smells of political interference and is against DoJ policy,” Becker said, noting that state officials are following Alaska’s election laws and that the federal government does not have authority over certification timing or procedures. He added that courts would likely reject the suit.

The lawsuit argues that if Senator Sullivan loses, there is a chance the result was affected by votes cast for Daniel J. Sullivan Jr. The complaint states that if all votes cast for the latter had gone to the incumbent, then Sullivan would have won under Alaska’s ranked-choice voting system. It requests that Alaska not certify election results until such potential voter confusion is resolved.

The ranked-choice voting system in Alaska allows voters to rank candidates by preference, with subsequent tallies used if no candidate achieves a majority in the first count. This method adds complexity to the tabulation and certification process, particularly in close races.

Democrats have denied any connection to Daniel J. Sullivan Jr., who has maintained that he is running as a moderate Republican out of dissatisfaction with Senator Sullivan’s record. He said his intention is not to mislead voters.

The lawsuit marks the latest in a series of legal efforts by the Trump administration to influence the outcome of midterm elections, a significant point as control of Congress remains highly contested. Election administration is traditionally managed by state and local authorities, but the federal government’s increased litigation in several states has raised concern among election experts about political interference.