FBI agents have questioned campaign donors in Petersburg, Alaska, as federal authorities investigate allegations that Democratic campaigners recruited candidates to compete against Republican Sen. Dan S. Sullivan. Among those drawing scrutiny is Dan J. Sullivan, a former elementary school teacher whose friends say they have not seen him for weeks.

The Trump administration is considering criminal charges involving a tactic known as ballot stacking, in which candidates are recruited to divert votes from an opponent. The investigation comes as the incumbent Sullivan faces a strong challenge from Democrat Mary Peltola, a former U.S. representative, in a contest that could help decide control of the Senate.

Peltola has denied involvement. A New York Times report published last week connected a group supporting her to a Democratic operative seeking to recruit decoy candidates. At an Anchorage rally last week, Peltola rejected such tactics. Dan J. Sullivan also denied outside involvement when interviewed by The Associated Press in June, saying he had no contact with Peltola's campaign and had not been approached by Democratic operatives about running.

On Sunday, a federal judge dismissed a Trump administration lawsuit seeking to renew efforts against the teacher's candidacy and block certification of election results, potentially challenging a Peltola victory. The Justice Department promptly appealed. Earlier, the Alaska Division of Elections had attempted to remove Dan J. Sullivan from the primary ballot after finding that he had not entered as a Republican in good faith. State courts overturned that decision. Election officials distinguish the senator on the ballot by identifying him as the Republican incumbent.

The criminal investigation has been underway for months, with agents arriving in Petersburg in recent days. Most of the teacher's dozen campaign contributors live in the town, and their donations totaled $7,150. Donors interviewed by AP said agents asked whether they had been misled. Anna Holmes, who contributed $500 with her husband, said agents visited Friday night and described their inquiry as involving campaign finance violations. They also asked whether the couple had meant to support the senator.

Sharon Hunter, who donated $1,000 with her husband, questioned the use of federal resources after agents visited Saturday. Other supporters pointed to Sullivan's contributions to the community. Retired fisherman Ed Wood said his $1,000 donation reflected gratitude for help Sullivan and his wife provided during a decade-long fight against logging on a hillside above Petersburg. Residents also recalled his after-school guitar program, Little Kids Rock.

Some residents were less sympathetic. Amanda Ohmer said she was surprised that her son's former teacher, whom she regarded as a well-known liberal, entered the race as a Republican in May, three days after Peltola visited Petersburg. Ohmer supported the investigation. Donor Charles Flint described Sullivan as a liberal thinker who sometimes backed Republicans, but said Sullivan never explained his decision to run.

Petersburg, a fishing town of 3,000 known as Little Norway, has become a focus of federal and media attention. AP has been unable to reach Dan J. Sullivan since the Times report. Alaska has a history of efforts to promote candidates who might draw votes from rivals, while its open primary and ranked choice voting system add complexity to the contest. About 60% of the state's 600,000 registered voters identify as independents.