President Trump on Wednesday endorsed Mike Lindell, the chief executive of My Pillow, in a bid to be governor of Minnesota, throwing his support behind a candidate best known for promoting the falsehood that voting machines in the United States are often rigged and have flipped elections. Mr. Trump called Mr. Lindell “one of America’s greatest and most hard working Patriots” in a post on his social media site.

The endorsement jolted a race that has been upended by the president’s focus on the state. After the Trump administration began an immigration crackdown in the state while railing against fraud in social services programs, Gov. Tim Walz, a Democrat, abandoned his bid for a third term late last year. Senator Amy Klobuchar, a popular Democrat with a history of winning by double-digit margins, announced a bid early this year and is seen as a formidable opponent. Mr. Lindell faces two main rivals in a Republican primary next month: Kendall Qualls, a businessman who won the endorsement of the state Republican Party, and Lisa Demuth, the speaker of the Minnesota House of Representatives.

Mr. Lindell has been among the most vocal figures sowing doubt about the reliability of voting machines and was an outspoken supporter of Tina Peters, a county clerk in Colorado who was convicted of tampering with voting machines. Last year, a jury in Denver found that Mr. Lindell had defamed a former employee of Dominion Voting Systems and ordered him to pay $2.3 million in damages. In this primary season, Mr. Trump has had a mixed record of success with candidates he has endorsed.