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The leader of one of the nation’s oldest and largest unions stunned political observers by issuing a surprise endorsement for a Senate Republican stalwart over the weekend.

Teamsters General President Sean O’Brien, who famously nearly came to blows with now-Secretary of Homeland Security Markwayne Mullin during a Senate hearing before ultimately becoming acquaintances, issued a ringing endorsement of Sen. Ashley Moody, R-Fla., signaling a major break from national union sentiment that has tended to favor Democrats.

"Just voted in the State of Florida for the first time, and very proud to have cast a ballot for Sen. Ashley Moody," O’Brien, whose 123-year-old union is about 1.3 million-strong, announced Sunday.

5 TAKEAWAYS FROM FLORIDA SENATE PRIMARY: GOP SEN ASHLEY MOODY WILL FACE DSA'S NIXON

"Sen.…