Former Sen. Jim Abdnor, who shocked liberal America in 1980 when he defeated Sen. George McGovern only to be ousted himself six years later, died Wednesday at the age of 89.

The South Dakota Republican was best known for his dramatic 19-point defeat of the iconic McGovern. McGovern, who ran for president as the Democratic nominee in 1972, remained an influential force in the Senate and in Democratic politics, and his defeat at the hands of Abdnor marked the end of an era for his party and heralded the Reagan revolution on Capitol Hill.

A World War II veteran, Abdnor spent nearly 40 years in politics, beginning in 1951 when he served as first assistant chief clerk in the South Dakota House.

From then on, Abdnor became increasingly involved in state and local Republican politics, and in 1956 he won a seat in the state Senate. In 1968, he won election as lieutenant governor.

Following an unsuccessful bid for the House in 1970, Abdnor won an open House seat in 1972.

During his time in the House, Abdnor made a name for himself on farm policy issues as well as spending, becoming part of a generation of Republicans who melded deeply conservative notions about government with the traditional view of legislating and compromise.

Then came his surprising defeat of McGovern in 1980. Over the next six years, Abdnor would continue to mix conservative ideals with a respect for the legislative processes of the Senate.

But his time in the chamber was short-lived. He was defeated by then-Rep. Tom Daschle in a race widely seen as the revenge of the Democratic Party’s liberal wing, although 1986 was a good year overall for Democrats. Eighteen years later, Daschle, who had by then risen to Senate Minority Leader and had also served as Majority Leader, would lose to yet another young upstart, now-Sen. John Thune (R). Abdnor mentored Thune during much of his political career.

South Dakota politicians of all stripes lauded Abdnor’s impact on the state.

“Everything I know about politics that is good I learned from Jim Abdnor. He was a hardworking and effective fighter for South Dakota, and one of the most decent and genuine people to ever hold elective office,” Thune said in a statement.

“I came to know Jim through our mutual love of sports and have been blessed to have him as a mentor and a role model. Kimberley and I and our daughters, who Jim treated as his own, will always remember Jim’s friendship and mentoring and his boundless love for South Dakota. He was a mentor and a friend and I will miss him greatly,” added Thune, who worked for Abdnor in the Senate as a legislative assistant. Abdnor was President Ronald Reagan’s pick to lead the Small Business Administration after his 1986 loss, and Thune worked for him there as well.

Daschle also praised his former opponent.

“Jim Abdnor earned the respect and admiration of everyone who had the good fortune to know or work with him, including me. South Dakota had no better advocate. He was a dedicated and devoted public servant who encouraged public service in others, too. I am deeply saddened by the news of his death,” Daschle said in a statement.