Former U.S. Senator David Durenberger, a Minnesota Republican who espoused a progressive brand of politics and criticized the GOP after his political career, died Tuesday at age 88.

Durenberger’s health had declined in recent months, his longtime spokesperson Tom Horner said. Horner told The Associated Press that Durenberger died Tuesday morning of natural causes. He was at his St. Paul home surrounded by family.

Durenberger — a former executive secretary to GOP Gov. Harold LeVander, former corporate attorney and former captain in the U.S. Army Reserve — won a U.S. Senate seat in 1978. He served three terms and championed health care reform. He pushed proposals to expand Medicare benefits, protect rights for disabled people, including the landmark Americans with Disabilities Act, and to promote gender equity.

"Senator Dave Durenberger was a true public servant," Democratic U.S. Sen. Amy Klobuchar, of Minnesota, said in a statement. Klobuchar, who holds Durenberger’s old seat, said he had personally showed her much kindness when she was first elected in 2006.

"He was a dedicated legislator who was always guided by his devotion to bipartisanship and improving people’s lives," Klobuchar said. "His work to advance the Americans with Disabilities Act and prohibit discrimination against people with disabilities changed millions of lives for the better and made our nation stronger."

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Durenberger’s first wife, Judy, died of breast cancer in 1970, leaving him a widower raising four sons. Dave Durenberger, his son, said he stayed an active father, attending their athletic matches.

When he ran for office in the late 1970′s, his sons helped stuff envelopes at their dining room table, joined parades and helped on the campaign.

"He was sort of our north star for how we needed to live our lives," Dave Durenberger said.

As he rose through the Senate, Durenberger went through troubled periods in his personal life. He separated from his wife, Penny, in 1985 -- a personal agony he openly discussed with several reporters at the time. He married Susan Foote, a former member of his staff, in 1995.

Dave Durenberger said his father in recent years was a frequent presence at his grandchildren’s school and sports events. Durenberger showed his family how to value people, regardless of their social status, he said.

"He tried to find the goodness or the common bond that he shared with everybody. Everybody had the potential to be his friend -- whether it was the King of Jordan or the Jordanian immigrant driving a cab," Dave Durenberger said.

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But Senator Durenberger's career took a downturn in 1990. He was unanimously censured by the Senate following an Ethics Committee investigation into payments he received for book royalties and federal reimbursements for stays in a Minneapolis condo. In 1995, Durenberger also pleaded guilty to five misdemeanor charges related to the condo payments.

"If there is a smudge on the Seal of the United States Senate, or on the Star of the North, as we like to call our state, I will work my hardest to polish both back to brightness," Durenberger told his Senate colleagues after his censure.

He decided not to run for reelection in 1994. Following his exit from politics, he worked with a number of initiatives focused on health care policy. As chair of the National Institute of Health Policy at the University of St. Thomas Opus College of Business, he addressed systemic health care problems.

As the Republican Party tilted toward fiscal conservatives focused on slashing government programs, Durenberger became a critic. He told a Minnesota political podcast in 2005 that Democrats are "better equipped to carry the day" on health care policy, though he said at the time he would not become a Democrat.

In the 2016 and 2020 presidential elections, he endorsed Democrats Hillary Clinton and Joe Biden over Donald Trump. And in 2018, he wrote a book with political reporter Lori Sturdevant titled, "When Republicans Were Progressive." It mourned a nearly-extinct wing of the GOP in which lawmakers prided themselves on bipartisanship and sought to assist vulnerable people.

Horner said services will be held next week at Durenberger's alma mater, St. John's University in Collegeville.