Updated 7:58 p.m. | Republican Rep. Darrell Issa is retiring after nine terms in Congress, opening up a competitive House seat in California.

“While my service to California’s 49th District will be coming to an end, I will continue advocating on behalf of the causes that are most important to me, advancing public policy where I believe I can make a true and lasting difference, and continuing the fight to make our incredible nation an even better place to call home,” the congressman said in a statement Wednesday.

Issa was one of the most vulnerable House incumbents this cycle. He was first elected in 2000 and previously chaired the Oversight and Government Reform Committee.

The California Republican narrowly won re-election in 2016, defeating Democrat Doug Applegate 50.3 percent to 49.7 percent. Hillary Clinton carried his district by 8 points, according to calculations by Daily Kos Elections. But Issa said his internal polling showed he would have been re-elected. 

The race will likely attract attention and money, with billionaire Democratic donor Tom Steyer saying Monday he would target the district as part of a broader effort to flip the House. 

“If Tom Steyer thinks he can bring money? Bring it on,” Issa told reporters Wednesday. “I intend on staying very involved in both contributing my time and money.”

The congressman regularly topped the list of the richest lawmakers, making his fortune in the car alarm business before being elected to Congress.

Republican Mitt Romney carried the district by 7 points in 2012, while former President Barack Obama took it by 2 points in 2008. The GOP has a voter registration advantage here, according to February 2017 data from the California secretary of state. Republicans make up roughly 37 percent of registered voters while 31 percent are Democrats. A quarter of voters are not registered with either party.

The 49th District in southern Orange County was already a top target for Democrats hoping to win back the House. Inside Elections with Nathan L. Gonzales rates the race a Toss-up.

“Secretary Clinton won this district by a huge margin in 2016, and the cohort of strong Democratic challengers, unprecedented grassroots activism, and historic investment by the DCCC in Southern California means we are in a strong position to elect a Democrat to the 49th District this fall,” Drew Godinich, spokesman for the Democratic Congressional Campaign Committee, said in a statement.

The DCCC is heavily targeting Republican-held districts in Southern California. The committee opened an office in Orange County last spring, and invested in the state party to hire organizers in the 49th, 39th and 10th districts. GOP Rep. Ed Royce in the 39th District announced his retirement Monday.

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Republicans have also been active in the Golden State. The Congressional Leadership Fund, a super PAC aligned with House GOP leadership, has opened field offices in five districts, including three in Southern California. CLF also has offices in the 21st District in the Central Valley and in the 10th District in Northern California.

GOP Assemblyman Rocky Chávez, a former Marine, jumped into the race a few hours after Issa’s announcement, pointing out in a press release that his state assembly district includes portions of San Diego and Orange counties.

Also seeking Issa’s seat is Republican Diane Harkey, chairwoman of the state Board of Equalization and a former assemblywoman. She set up a fundraising committee with the Federal Election  Commission on Wednesday.

A GOP source named San Diego Mayor Kevin Faulconer as a potential candidate.

Republicans are hopeful a crowded Democratic primary will result in a weakened general election candidate.

“While Democrats fight with each other, Republicans will focus on fighting Democrats — and that’s how we plan to win,” said Ohio Rep. Steve Stivers, chairman of the National Republican Congressional Committee. “We look forward to facing whoever limps out of the Democrats’ battle royale: black and blue, and broke.”

Four Democrats were already vying to take on Issa.

Applegate, a Marine veteran and the 2016 nominee, is running again. Real estate investor and Navy veteran Paul Kerr is also in the race, along with environmental lawyer Mike Levin and Sara Jacobs, who worked at the State Department and the United Nations.

All candidates will face off in the June 5 primary. Under California’s unique primary system, the top two vote-getters, regardless of party, advance to the general election.

Lindsey McPherson contributed to this report.