The US Department of Justice has expanded its investigation into Alaska’s Senate election, sending target letters to several people as President Donald Trump’s administration pursues allegations that Democrats fielded a sham candidate. The administration says the candidate was intended to confuse voters and cause the incumbent Republican senator to lose, an accusation Democrats deny.

Attorney Marc Elias, who has represented the Democratic Party, was among those sent letters by federal prosecutors on Tuesday. The notices indicate that prosecutors believe they have gathered enough evidence connecting the recipients to a possible crime to consider them potential defendants in a future indictment. The letters mark a further step in the investigation into the disputed allegations surrounding the race.

The contest pits incumbent Republican Senator Dan Sullivan against Mary Peltola, a former Democratic congresswoman, in the midterm elections. Their race could be pivotal to deciding which party controls the Senate. Another candidate on the ballot is also named Dan Sullivan, and his participation is at the center of the administration’s accusations about an effort to mislead voters.

Trump and officials in his administration allege that the Democratic Party deliberately encouraged the newcomer Sullivan to run because he shares the incumbent’s name. They say the purpose was to create confusion on Election Day. Democrats reject that account and maintain that Tuesday’s ballots clearly distinguish between the two candidates named Dan Sullivan.

The Justice Department previously sought a court order that would have blocked certification of Alaska’s election if the incumbent Sullivan lost. That effort was unsuccessful. The department has nevertheless continued its investigation into the alleged scheme involving the other candidate with the same name.

The Associated Press reported that investigators had issued more than 100 subpoenas as part of the inquiry. Its report cited an unnamed person who had been briefed on the investigation, which has now also brought target letters to Elias and other recipients.

In a statement issued Tuesday, Elias criticized the department for targeting him and his law firm on Election Day. He described the inquiry as a “sham investigation” and said it would not intimidate them. Elias also said his firm would continue working around the clock to support its clients and seek electoral defeats for Trump’s party.