Sen. Pat Roberts, the long-serving Kansas Republican, announced Friday that he will not seek re-election in 2020 and will retire at the end of his term.

Roberts, 82, has had a venerable career in Congress, representing Kansans for 16 years in the House and 22 years so far in the Senate.

"Never in my wildest dreams did I think I would become the longest-serving member of Congress in our state’s history," Roberts said at a news conference in Manhattan, Kansas.

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Roberts serves as chairman of the Senate Committee on Agriculture, Nutrition and Forestry and has been an outspoken advocate for farmers. He led the charge in getting the $867 billion farm bill passed last year with bipartisan support. He also chaired the Senate Select Committee on Intelligence from 2003 to 2006.

"As I considered this decision, I reflected on whether after nearly 40 years, I could stand before you and say that I had made a difference for Kansas and the country," he said. "Here today, in Manhattan, we can see this was true and I am proud to have had a part in making a difference, a part in making it better."

Roberts decision not seek a fifth term comes during a politically fraught time in the state. In the 2018 midterms, Democrat Laura Kelly was elected governor and Democrat Sharice Davids won a congressional seat. Also, three female moderate Republican state lawmakers have since switched parties, citing their frustration with the direction of the GOP under President Donald Trump.

Roberts himself faced a tough primary challenge in 2014 against a newcomer and Tea Party candidate, receiving less than 50 percent of the vote.

In his speech on Friday, Roberts said that he was proud of his record and vowed to continue his work until his term ends.

"Think of all the dedicated public servants I have worked with and, not to get partisan, think of all the competitors and political personalities who have come and gone. We outlasted most of them and made genuine friends with many along the way," he said.

"Despite the partisan division and conflict in Washington that threatens progress, I continue to believe we can achieve results. Those who know me know — I work hard, I persevere, I do not give up and I will do what it takes to get the job done. Experience counts."

Potential Republicans who could replace Roberts, according to The Associated Press, include departing Gov. Jeff Colyer, outgoing Kansas Secretary of State Kris Kobach, who lost to Kelly in the governor's race, and Rep. Roger Marshall, who holds the same western Kansas seat Roberts once did. Among Democrats, Barry Grissom, a former U.S. attorney for Kansas, was considering the race before Roberts' announcement.