Speaker Paul D. Ryan’s decision not to run for re-election opens up the race for his seat in southeast Wisconsin, which Democrats are targeting this year.

Ryan, who was first elected in 1998, said Wednesday he could not in good conscience ask 1st District voters for their support when he was not going to stay in Congress.

“For me to ask them to vote to re-elect me knowing I wasn’t going to stay is simply not being honest,” the Wisconsin Republican said.

His decision could spark a potentially crowded GOP primary for his seat. The filing deadline is June 1 and the primary will take place Aug. 14.

“There has been a pretty fast fury of names discussed this morning in Republican circles,” one GOP operative with experience in Wisconsin said.

Watch: A Look Back at Paul Ryan’s Career in the House

Two of some of the most discussed potential contenders include state Assembly Speaker Robin Vos and Bryan Steil, a lawyer and member of the University of Wisconsin Board of Regents. State Sen. David Craig, who used to work for Ryan, was also mentioned as a potential candidate.

State Rep. Tyler August, the Assembly speaker pro tempore, was also mentioned as a possible candidate. He previously chaired the Republican Party in the 1st District. State Rep. Samantha Kerkman was also named as a possible contender. A GOP memo on the district shared with Roll Call also named Reince Priebus, the former Republican National Committee chairman and White House chief of staff, as a candidate who “could easily mount a credible campaign if he so desired.”

Ryan does not have any plans to endorse in the GOP primary, said Kevin Seifert, the executive director of Team Ryan, the speaker’s political operation.

“There are many qualified conservatives in Southern Wisconsin and Speaker Ryan and his team will work tirelessly so Republicans keep this seat,” Seifert said.

But Seifert did say that Paul Nehlen, who was waging another long-shot primary challenge to Ryan, was not a suitable alternative. Nehlen has been accused of making racist and anti-Semitic remarks.

“His bigoted rhetoric and his reprehensible statements should disqualify him from holding any public office and we are confident voters in Southern Wisconsin feel the same way,” Seifert said of Nehlen.

Republicans are confident they will hold onto the seat, even with a well-funded Democrat already running. Ironworker Randy Bryce has raised $4.75 million since jumping into the race, his campaign announced earlier this month. That includes $2.1 million in the first quarter this year.

Watch: Ryan Announces He Will Not Seek Re-election

Bryce was named to the Democratic Congressional Campaign Committee’s “Red to Blue” program for promising candidates, which provides additional committee support. Janesville school board member Cathy Myers is also running in the Democratic primary.

But Bryce still lagged Ryan in his cash haul. A prolific fundraiser, Ryan had $10.6 million in his campaign coffers at the end of 2017.

The GOP operative said the eventual Republican nominee would still be able to tap into the Wisconsin donor network, and raise enough money to compete.

Republicans have carried the seat in the last two presidential contests: President Donald Trumpby 10 points in 2016 and Mitt Romney by 5 points in 2012, when Ryan was on the ballot as the vice presidential nominee. Former President Barack Obama carried the district by 3 points in 2008.

Bryce’s campaign said in a statement Wednesday that the 1st District is not as conservative as it might appear. The campaign noted that Trump winning margin here was smaller than his 2016 edge in Pennsylvania’s 18th District, where Democrat Conor Lamb won a special election last month.

“Paul Ryan decided to quit today rather than face Randy Bryce and the voters,” Bryce campaign spokeswoman Lauren Hitt said. “With nearly $5 million raised to date, a strong field program aided by organized labor, a broad coalition of support locally and nationally, Randy Bryce is incredibly well positioned to be the next representative for the First District.”

Myers, the other Democrat in the race, also said Ryan “is running away from the harm his policies have caused our neighbors in Wisconsin’s First District.”

“I am prepared to lead where Paul Ryan has failed to act,” she said.

Republicans disagree.

“Speaker Ryan’s unparalleled record of selfless leadership and dedication to Wisconsin’s 1st District is an inspiration for us all,” National Republican Congressional Committee spokesman Chris Martin said. “Republicans will hold this seat in November and continue to build upon his historic achievements.”

A GOP memo on the race shared with Roll Call detailed the district’s history of backing Republicans, including in a recent race for the Wisconsin Supreme Court. Republicans also note that having GOP Gov. Scott Walker at the top of the ticket this year will drive out GOP voters, especially in the 1st District where Walker is from.

Ryan was ahead of Bryce in recent polling, according to a Republican source.

A poll conducted by GOP polling firm Public Opinion Strategies found 55 percent of 1st District voters supported Ryan, compared to 34 percent for Bryce. The poll surveyed 400 likely voters in the district between March 18 to 20 by cell phone. The margin of error was 4.9 percentage points. 

Fifty-three percent of those surveyed had a “favorable impression” of Ryan, and 53 percent approved of Trump, according to the polling memo. The poll also tested a generic Republican against a generic Democrat. Forty-eight percent of those surveyed backed the Republican, compared to 36 percent for the Democrat.