State Senator Dino Rossi on Thursday announced his run for the 8th Congressional District to replace Republican Dave Reichert, who is retiring at the end of his term.

Rossi made the announcement during the annual Washington State Republican Party Dinner Thursday night in Bellevue. Rossi launched his website, which confirmed his run for Congress.

A resident of Sammamish, Rossi was appointed last year to fill the vacancy left by the late State Senator Andy Hill.

Rossi himself served as an elected member of the Washington state senate from 1997 to 2003, where he chaired the powerful Ways and Means Committee.

He is also known as a former statewide candidate who narrowly lost the closest gubernatorial race in U.S. history.

Initially certified as Washington’s Governor-elect in 2004, Rossi ended up losing to Governor Chris Gregoire in a lengthy recount battle that ended in the courts

Rossi ran for governor again in 2008, then for Senate in 2010, but lost both subsequent statewide races.

The congressional race he now enters is considered a “toss-up” by the Independent Cook Political Report.

The district, which includes eastern parts of King and Pierce Counties, has, so far, always elected Republicans to Congress, but was carried by Hillary Clinton in 2016 and former President Obama in 2012.

In 2012, redistricting extended the district east across the Cascades, making it safer for Republican candidates. However, Democratic operatives believe the current political climate in Washington D.C. makes the seat a prime “pick-up opportunity.”

Several Democratic challengers have already announced their campaigns, including Issaquah Councilmember Tola Marts, pediatrician Dr. Kim Schrier, former King County Deputy Prosecutor Jason Rittereiser, Amazon software developer Toby Whitney, a former legislative director for former Congressman Jim McDermott, and business owner Mona Das.

With Congressman Reichert’s decision not to seek re-election, the race will quickly become one of the most competitively and closely watched next year, ahead of the 2018 midterms.

Democrats need 24 seats to win back a majority in the U.S. House.

In a previous interview with KING 5, Congressman Reichert acknowledged it will be a fierce election season next year.

"Before this announcement, people were saying this is Dave Reichert’s district, it’s his to win again. After this announcement, the pundits have been saying this now leans to a Democrat, and I think that could be correct, considering the traveling that I’ve done in the district, in talking to people," said Reichert. "The feel, the gut feeling that I have is there is a lean to the left. Not a strong lean, but there is a lean there, and I think there’s an opportunity. It’s going to be a tough battle."

The Washington State Democratic Party considers the race a priority and plans to step up organizing activities ahead of the campaign season.

"We’re launching three intensive volunteer organizing academies over the next two weeks to gear up for this fight," said State Party Chair Tina Podlodowski, following Reichert's announcement. "It’s time we flip the 8th."

Republicans, meanwhile, hope the right candidate will help them hold onto the seat.

“Dave Reichert is a valued voice whose unique perspective serving as King County Sheriff before coming to Congress will be missed within our House Republican Conference,” said National Republican Congressional Committee Chairman Steve Stivers in a statement.

“Nonetheless, Washington’s Eighth District is a seat that has chosen Republicans for over a decade. 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.”