President Barack Obama signs a bill on May 19, 2015, in the Oval Office. Rep. Dave Reichert stands directly behind him with arms on the chair. (Pablo Martinez Monsivais/AP)

Rep. Dave Reichert (R-Wash.), a seven-term moderate from Seattle’s suburbs, will leave Congress at the end of 2018, creating a political opportunity for Democrats.

“After spending time during the August work period with family and friends, reflecting on the past, discussing the future, and celebrating another birthday, I have decided this will be my last term,” Reichert said in a statement. He turned 67 last month.

Reichert was elected in 2004 and is one of 23 Republicans who represents a district where voters picked Hillary Clinton for president over Donald Trump. The 2016 election, however, was one of very few where Democrats did not give him a direct challenge. From 2004 to 2010, he never won more than 53 percent of the vote, as Democrats tried but failed to overwhelm the district’s rural Republican vote with liberals from eastern King and Pierce counties.

Reichert’s personal qualities proved difficult for Democrats to overcome. An Air Force veteran, he spent 30 years in the King County sheriff’s department, becoming sheriff himself in 1997. He gained national fame as a member of the task force that captured the “Green River Killer,” one of the era’s deadliest mass murderers. And in Congress, he often sided with his party’s centrists, most recently casting one of 20 Republican “no” votes against the effort to repeal the Affordable Care Act.

In 2012, a new congressional map kept Reichert in a swing seat, which he continued to win — by bigger margins. In 2016, while Donald Trump won just 44.7 percent of the vote in the 8th District, Reichert took 60.2 percent of the vote against nominal opposition.

This year, Democrats had already put the 8th District on their target list, and eight Democrats had piled in to run against him. That could complicate the party’s chances of victory. Washington, like California and Louisiana, now has a top-two primary system where the general election is fought between the biggest vote getters in a primary, no matter their party. In 2016, a strong year for Washington Democrats, the party lost control of the state treasurer’s office when three Democrats split their vote, allowing two Republicans to face off for the prize.

“With a bitter and expensive primary fight already confronting Democrats in this seat, Republicans are ready to elect another common-sense congressman like Dave Reichert, not another rubber stamp for Nancy Pelosi,” said Rep. Steve Stivers (R-Ohio), the chairman of the National Republican Congressional Committee, in a statement.

Democrats have had better luck this year in getting their preferred candidates past crowded primaries. In Georgia’s 6th District, Democrat Jon Ossoff nearly won an April “jungle primary” with more than 50 percent of the vote, despite the presence of lesser-known Democrats on the ballot. Last month, Democrat Doug Jones easily won a primary for Alabama’s December U.S. Senate race, fending off several challengers whom the party saw as unelectable.

But veteran GOP advisers are waiting to see if this is the first of a string of retirement announcements, as the congressional session has produced little legislative results to tout, and looks like the 2018 midterms could be difficult for Republicans. Reichert is the 12th Republican to leave the House since the start of 2017. Four took jobs in the Trump administration; three are running for governor in their home states. Reichert is the fifth to simply enter retirement, and the second, in addition to Rep. Ileana Ros-Lehtinen (R-Fla.), to do so in a seat won by Clinton.

By contrast, just seven Democrats have left or announced plans to leave the House, and all but one — Rep. Niki Tsongas (D-Mass.) — did so to seek higher office. Rep. Tim Walz (D-Minn.) is the one Democrat to have vacated a seat whose voters backed Trump in 2016.

Paul Kane contributed reporting.