He is possibly one of the most popular politicians in the United States — Duke the dog has been elected as mayor of his Minnesotan town for the third time.

Duke was sworn in for his third year-long term in Cormorant, his town of about 1,000 residents, on the weekend.

"Everybody voted for Duke — except for one vote for his girlfriend, Lassie", according to Duke's owner, David Rick.

The nine-year-old great Pyrenees was first elected in 2014 with 12 write-in votes at the town's annual Cormorant Daze festival.

"I don't know who would run against him," Karen Nelson said. ( Twitter: Karen Nelson )

Even his human opponent at the time, Richard Sherbrook, admitted he voted for the canine.

"He's done such great things for the community," Karen Nelson, who describes herself as "Mayor Duke's caretaker", said.

"I don't know who would run against him."

The mayor could not be reached for comment.