Sen. Mike Enzi, R-Wyo., announced Saturday that he will not run for a fifth term in the Senate in 2020, leaving the seat open for candidates, including Rep. Liz Cheney, R-Wyo., who challenged him in 2014.

Enzi, 75, who is the chairman of the Senate Budget Committee, was sworn in as senator in 1997. He was elected to the Senate in 1996, replacing former Republican Sen. Al Simpson. He made the announcement in council chambers at Gillette’s city hall, the Gillette News Record reported. He is the former mayor of Gillette.

Enzi said he would spend the duration of his term centered on the budget reform, according to the Casper Star-Tribune.

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"I want to focus on budget reform,” he said, according to the paper. “I don't want to be burdened by the distractions of another campaign. After this year, I'll find other ways to serve."

According to his website, Enzi is also a member of the finance, health, education and labor committees, among others.

Wyoming Sen. Mike Enzi, R-Wyo., announced Saturday in the state he represents that he will not seek a fifth term in the Senate in 2020. (AP)

Cheney, the daughter of former Vice President Dick Cheney, challenged Enzi in 2014 but dropped her bid. Cheney currently sits as No. 3 in the House Republican leadership.

She released a statement regarding Enzi's retirement, saying he "devoted himself to serving our state and country."

"During his 20 years in Washington, he brought our state’s values to the nation’s capital, fighting for a smaller, less obstructive, and more efficient federal government that would allow people to grow and thrive," Cheney's statement read. "He recognized that empowering people, not politicians, was the best way to expand opportunity, and he worked tirelessly towards that goal."

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Fellow Republican Wyoming Sen. John Barrasso said in a statement: “Mike Enzi’s character, courage and credibility have made him a respected moral leader in the U.S. Senate. In four terms in the Senate, he has never wavered in his commitment to God, family or Wyoming.”

With Enzi's retirement, Wyoming will have its first open Senate seat in more than a decade.

The Associated Press contributed to this report.