Rep. Darrell Issa of California announced Wednesday he will not seek re-election, opening up another battleground in the deep blue state as Republicans and Democrats spar for control of the House.

His statement came two days after fellow Southern California Republican Rep. Ed Royce announced his retirement.

Republicans hold a 239 to 193 seat advantage in the House. Three seats are empty after member resignations. At least 30 House Republicans will retire or seek a different office, while about 15 Democrats will do so rather than seek re-election in the midterm elections.

"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," Issa said in the statement.

The conservative Issa, who joined Congress in 2001, only narrowly got re-elected to his seat in 2016. In the presidential race, Hillary Clinton won his district by 7 percentage points.

Billionaire Democratic activist Tom Steyer seized on the news of Issa's retirement as another sign that Republicans could be in trouble in the Nov. 6 midterm elections. "It shows that the Republican effort is losing some of its critical members," he said Wednesday on CNBC.

Earlier this week, Steyer launched a $30 million initiative to help Democrats flip seats and boost young-voter turnout in vulnerable districts for Republicans. Issa's district is one of the areas Steyer is targeting.

Democrats see numerous chances to pick up seats and potentially gain control of the House, partly driven by President Donald Trump's low approval ratings. Democrats have led Republicans by more than 10 points in an average of recent ballots that ask voters to choose between a generic member of both parties in 2018, according to RealClearPolitics.

Issa, who was a businessman before he entered politics, consistently ranked as one of the wealthiest members of Congress.

Issa gained notoriety as a thorn in the side of the Obama administration when he chaired the House Oversight and Government Reform Committee.

Royce, who has held his seat since 1993 and is chairman of the House Foreign Affairs Committee, was term limited in his leadership of the panel. He won his 39th Congressional District by about 15 percentage points in 2016.