LOS ANGELES — A political committee backed by billionaire Michael Bloomberg is spending nearly $9 million on TV ads to help two Democrats trying to topple Republican incumbents in Southern California.

Bloomberg disclosed earlier this year that he intended to spend tens of millions of dollars to support Democratic congressional candidates across the country as the party attempts to seize control of the House.

Federal records Thursday showed Independence USA is investing more than $4 million on TV ads opposing Rep. Dana Rohrabacher in Orange County’s 48th Congressional District, one of the most closely watched races in the nation. The 15-term congressman is in a toss-up contest with Democrat Harley Rouda.

The super PAC also invested more than $4.5 million on ads supporting Democrat Katie Hill, who is trying to oust Rep. Steve Knight in the 25th District north of Los Angeles.

The districts have been targeted by national Democrats trying to pick up 23 seats nationwide to win control of the House. They are among a string of Republican-held districts in California carried by Hillary Clinton in the 2016 presidential election.

Rouda has been critical of Rohrabacher’s skepticism about the cause of climate change. He said he believed Bloomberg’s involvement in the race reflected the former mayor’s concern with the congressman’s “extreme” positions, including on global warming.

Rouda said he’s never met Bloomberg “but I do thank him.”

Rohrabacher spokesman Dale Neugebauer said in an email that “billionaires from San Francisco and New York City are pouring millions of dollars into this district to buy the election for (House Democratic leader) Nancy Pelosi and advance their own personal agendas.”

“Their attack ads are intended to mislead and to distort Rep. Rohrabacher’s record. It won’t work. Voters here know and trust Dana,” he added.

Bloomberg’s committee earlier spent $1 about million on internet advertising in the two districts.

Howard Wolfson, a Bloomberg senior adviser, said in a text that Rouda and Hill were in a strong position to capture the seats against “out of touch incumbents.”

Bloomberg’s investment comes as money floods into competitive House districts in California from both Democratic and Republican groups.