A defamation lawsuit against a Minnesota legislator will head back to district court after the Minnesota Supreme Court denied a yearslong effort to get the case dismissed.

The high court ruled Wednesday that Rep. John Lesch, DFL-St. Paul, was not protected by the state Constitution’s guarantee of legislative immunity when he wrote a letter to Mayor Melvin Carter in January 2018 expressing concerns about Carter’s choice of Lyndsey Olson for city attorney — a letter that Olson later claimed was defamatory.

In her opinion, Chief Justice Lorie Gildea wrote that “nothing in the letter indicates that Lesch was acting pursuant to his duties as a legislator.”

“The letter does not become de facto legislative activity simply because Lesch sent it on his official letterhead,” she wrote.

In the letter, Lesch questioned Carter’s process for hiring department heads and said that, had he known Olson was being considered for the city attorney job, he “would have registered grave concerns over her fit for the office.” He went on to describe Olson as “a prosecutor who would sacrifice justice in pursuit of a political win.”

Lesch worked in the City Attorney’s office for about 15 years and previously applied for the top job. He also previously served in the Minnesota National Guard, where Olson was the first woman to serve as general counsel and deputy staff judge advocate.

Olson sued Lesch for defamation in February 2018, alleging he began a campaign to attack her credentials soon after Carter announced he was appointing her to the position.

Lesch sought to have the case dismissed, arguing that his letter was protected legislative activity. A Hennepin County judge denied Lesch’s motion to dismiss in September 2018, and the Court of Appeals agreed.

Lisa Lamm Bachman, Olson’s attorney, applauded the Supreme Court’s decision.

“We believe the Minnesota Supreme Court reached the proper conclusion based on both the well-established case law, federal case law, and also just on the content of the letter and how legislative immunity is interpreted and applied,” she said.

The case will go back to district court for discovery, which could take several months, Lamm Bachman said.

“We do intend to move forward through the discovery process,” said Marshall Tanick, Lesch’s attorney. “We are confident that ultimately the lawsuit will fail on both factual and legal grounds.”