DANA POINT, Calif.–Preaching to the choir, Sen. Marco Rubio (R-Fla.) told the Koch donor summit Sunday that the Environmental Protection Agency’s new clean energy rules will be “catastrophic” while making little difference on global carbon emissions.

Many of the 450 donors gathered at the oceanfront resort here have grown wealthy from the energy industry, including Charles and David Koch.

The presidential candidate got some of his loudest applause during a lunchtime Q&A session when he criticized the new rules that the federal government will formally unveil on Monday.

The crowd especially loved Rubio’s shot at Tom Steyer, the California billionaire who has invested heavily to counter the Koch network.

“It will make the cost of electricity higher for millions of Americans,” he said. “So if there’s some billionaire somewhere who is a pro environmental, cap-and-trade person, yeah, they can probably afford for their electric bill to go up a couple hundred dollars. But if you are a single mom in Tampa, Florida, and your electric bill goes up by $30 a month, that is catastrophic.”

Obama’s plan sets a goal of cutting carbon pollution from power plants by 32 percent by the year 2030, compared with 2005 levels.

But Rubio said this won’t really make a difference.

“Because as far as I can see, China and India and other developing countries are going to continue to burn anything they can get their hands on.”

Rubio said policy makers must balance the interests of economic growth against the environment.

The senator from Florida has appeared at Koch donor events several times since his first visit in January 2010, when he was taking on establishment favorite Charlie Crist, then the Republican governor, for their party’s Senate nomination.

Rubio won that year as a tea party favorite. He’s stood with the Koch network against crony capitalism when it came to voting against reauthorizing the Export-Import Bank and federally backed Terrorism Risk Insurance. But Rubio has raised the suspicions of movement conservatives by steadfastly supporting of special breaks for the sugar industry. The family that controls a huge swath of sugar production in the United States includes some of his major contributors.

Rubio steadfastly defended his protectionism, couching it in the same terms used by industry. He warned direly that Brazil would dominate sugar production if the United States took away the special breaks that industry gets.

“As soon as other countries get rid of theirs, we’ll get rid of ours,” he said.

The senator also said that, if elected to the White House, he would not use executive power the way that Obama has.

“I’m not going to use my pen and my phone as this president does,” he quipped.

On a hot day, Rubio removed his suit coat a third of the way through his half-hour appearance.

He defended his support for defunding Planned Parenthood.

Asked what has catapulted Donald Trump to the top of the polls, Rubio cited his steadfast opposition to “illegal immigration” among other things.

Rubio, who co-sponsored the 2013 Gang of Eight bill, said he still believes in reform but learned from that experience. “The lesson is you can’t do it in one massive piece of legislation,” he said, adding that new legislation cannot be passed until Americans are convinced that that illegal immigration is under control.

Rubio will be among the top 10 on stage for the first GOP debate this Thursday on Fox News. He declined to rule out the possibility of criticizing other Republicans, saying he is willing to point out areas of policy disagreement.

Asked by Politico’s Mike Allen what his posture will be on Thursday, Rubio deadpanned: “I’m going to be standing.”