Kansas GOP Sen. Pat Roberts announced Friday that he would not run for re-election in 2020, launching what is expected to be a competitive Republican primary for his seat. 

“I have had the honor and privilege of representing Kansas for 16 years in the House, 22 years so far in the Senate,” Roberts said at an event in Manhattan, Kansas, on Friday. “Never in my wildest dreams did I think I would become the longest serving member of Congress in Kansas history.”

Roberts, who was first elected to the Senate in 1996 after serving in the House, said he would serve out the rest of his term. He is currently the chairman of the Senate Agriculture, Nutrition and Forestry Committee.

Roberts, 82, faced the closest race of his career in 2014, when he fended off primary challenger Milton Wolf, who called the longtime lawmaker out of touch with Kansas.

Roberts won the primary by 8 points, but with 48 percent of the vote. He went on to win re-election by 9 points, defeating independent Greg Orman.

Despite winning the governor’s mansion and flipping a GOP-held House seat in Kansas in 2018, Democrats would likely face an uphill climb in an open Senate race. Kansans haven’t elected a Democrat to the Senate since 1932. President Donald Trump won the Sunflower State by 21 points in 2016.

Several names are already circulating as potential contenders on both sides. The Republican primary will likely be crowded, with one Kansas GOP strategist listing state Attorney General Derek Schmidt and outgoing Gov. Jeff Colyer as potential contenders. 

Colyer lost the GOP gubernatorial primary last year to Kansas Secretary of State Kris Kobach, a staunch ally of President Donald Trump. Kobach and state Chamber of Commerce President Alan Cobb are two other potential candidates, the Kansas City Star reported.

GOP Rep. Roger Marshall, who holds Roberts’ old House seat representing the 1st District, is also “seriously considering” running, according to his campaign manager Brent Robertson.

Robertson said Marshall, who was first elected in 2016, was “dead set on making sure we get border security funding to the president’s desk first. Until then, I don’t anticipate an official decision on a Senate run taking priority.” Part of the government is currently shut down amid a standoff over funding for Trump’s signature campaign promise: a wall on the southern border.

Former GOP Rep. Kevin Yoder, who lost re-election in the 3rd District last year, could also jump into the race, though one GOP strategist described the chances of Yoder running for the Senate as “slim.”

Multiple news outlets also floated Secretary of State Mike Pompeo’s name as a potential Senate contender. (Pompeo previously represented Kansas in Congress before joining the Trump administration.)

On the Democratic side, former U.S. Attorney Barry Grissom has expressed interest in running, telling McClatchy in December that he was considering challenging Roberts.

Brent Welder, who ran unsuccessfully for the Democratic nomination in the 3rd District, has also been rumored to be eyeing a run. Welder, a progressive labor lawyer, worked for Sen. Bernie Sanders’ presidential campaign in 2016, and was backed by Sanders and New York Democratic Rep. Alexandria Ocasio-Cortez in the crowded primary. Welder lost the primary to attorney Sharice Davids, who went on to defeat Yoder.

“While Brent has not made any decisions at this point, he is always looking for an opportunity to defend working families against the billionaires and giant corporations that are ruining the middle class economy and corrupting our government,” said Welder’s senior adviser Shawn Borich. 

Democratic strategist Zach Helder, who managed Democrat Tom Niermann’s unsuccessful primary campaign in the 3rd District, was not optimistic about his party’s chances of flipping this Senate seat despite some success in 2018. Helder said Welder, whose Kansas ties were questioned in the primary, should stay out of the Senate race or run for local office instead.

“People are trying to compare [the Senate race] to the governor’s race last cycle and it’s not an apples to apples comparison,” Helder said, referring to Democrat Laura Kelly defeating Kobach in 2018. “These Senate races get nationalized.”

“We just haven’t quite built the bench up to that point,” Helder said. “I think in six years we’ll have a real, actual credible shot at flipping a Senate seat. I just don’t think we’re quite there yet.”