US President Donald Trump is on the warpath over a “decoy” candidate with the same name as the incumbent Republican after a media report exposed he was recruited as a spoiler.

Two candidates named Dan Sullivan are up for election in Alaska, one of the tightest contests that could decide control of the US Senate.

Incumbent Republican Senator Dan S. Sullivan is running a close race against Democrat Mary Peltola.

But a third contender is another Republican named Dan J. Sullivan Jr.

The Republican Party had been claiming this “decoy Dan” was only running “with the intention ‌of misleading supporters of Senator ‌Sullivan into voting for him” and has already taken steps to have the results blocked if the outcome is close.

Now a report in The New York Times seems to confirm this after evidence emerged that Democrats had put out a search for people named Dan Sullivan in Alaska.

“The Times has found, based on interviews and text messages, along with documents prepared for a potential lawsuit against the campaign, that not only did Ms. Peltola’s team work with people trying to recruit Mr Sullivan to run for Senate, but the effort was much broader,” the paper wrote.

“The group worked to coax other would-be spoilers into the race, to dilute the incumbent’s support and help catapult the Democrat to victory.”

Trump blew up about the allegations in a post on Truth Social.

“It has just been determined that the Democrats in Alaska illegally searched for, and recruited, a man named Dan Sullivan to run against our distinguished Republican Senator, Dan Sullivan, in order to defraud, confuse, and obfuscate the Election, thereby taking votes away from the REAL Senator, Dan Sullivan,” he wrote.

“Mary Peltola should suffer the Legal and Political consequences for what she has done, A FRAUD ON THE AMERICAN PUBLIC, and Dan Sullivan should be allowed to run without either Mary Peltola or FAKE Dan Sullivan on the Ballot.”

Alaska Governor Mike Dunleavy, a Republican, said he was ordering an investigation to determine whether the alleged effort violated state law.

“Alaskans have a fundamental right to vote for the candidate they actually intend to support,” Dunleavy said in a statement.

“Deliberately tricking voters into casting their ballots for someone else strikes at the integrity of our elections.”

Earlier this week the US Justice Department sued to pre-emptively block Alaska from certifying the results if the Republican incumbent candidate lost by a narrow margin.

The lawsuit signalled the willingness of Trump’s administration to contest the results of the November 3 midterm elections that will decide control of the US Congress.

The ⁠lawsuit asks a federal judge to block the certification of an outcome “that may be impacted by voter confusion,” so that there can ​be “an investigation to determine whether votes cast for Daniel J. Sullivan were meant to be cast for Senator Sullivan.”

Trump told reporters he supported the lawsuit, saying “I’m the one that said do it.”

A Justice Department spokesperson said in a statement the agency was taking “necessary steps to ensure that this frivolous candidacy does not undermine the integrity of Alaska’s election or the will of its voters.”

Election officials around the US have told Reuters they are preparing for potential federal interference in November’s elections, including legal challenges and disputes over voting that could disrupt certification of the results.

Trump has a long history ⁠of challenging election outcomes and encouraging supporters to contest results he views as unfavourable.

The unelected Sullivan, a former US Forest Service worker and school teacher, filed to run as a candidate on May 29 seeking to unseat Senator Dan ​S. ​Sullivan and “put Alaska first,” according to his campaign website, which advertised “Dan Sullivan Challenges ​Dan Sullivan for US Senate Seat.”

Dan J. Sullivan has denied in interviews with US news outlets ‌that his aim is to cause confusion or divert votes from Dan S. Sullivan.

-with AAP