In Alaska this election season, the biggest supporters of Dan Sullivan could be the biggest antagonists of Dan Sullivan.

The field of contenders challenging Senator Dan S. Sullivan, a Republican who is up for re-election, has grown in recent days with a rather befuddling addition: Dan J. Sullivan, a former educator of no known relation, has entered the race.

His arrival could cause a headache for Senator Sullivan, who is working to fend off a challenge from former Representative Mary Peltola, a well-funded and independent-minded Democrat who says she is running on “fish, family and freedom.”

Dan J. Sullivan’s campaign announcement says he is a former elementary-school teacher and bartender from Petersburg, Alaska, a small town about 120 miles southeast of Juneau known locally for its Scandinavian spring festival. The announcement lays out no policies and does not describe his party affiliation.

The campaign arm of Senate Republicans, the National Republican Senatorial Committee, suggested that Dan J. Sullivan was a plant by Democrats intended to confuse voters and siphon support from Senator Sullivan, a former Marine who worked in the State Department under President George W. Bush.

If some voters mistakenly vote for Dan J. Sullivan thinking they’re voting for Senator Sullivan, it could make the difference in a tight race, political observers said.