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President Donald Trump — in his recent frenzy to push homeless people off the streets of California — just turned up the pressure on San Francisco and other liberal California cities he sees as “going to hell.”

Hours after Housing and Urban Development Secretary Ben Carson denied California’s plea for more federal aid Wednesday, Trump floated the idea of instead punishing San Francisco with an environmental violation — because the runoff of human waste and hypodermic needles pose a threat to the Pacific Ocean. (Experts told the San Francisco Chronicle the city hasn’t had any issues with needles in the water.)

“They have to clean it up,” Trump said of San Francisco as he left California aboard Air Force One Wednesday, according to the New York Times. “We can’t have our cities going to hell.” (San Francisco also falls within Democratic House Speaker Nancy Pelosi’s district.)

It’s unclear what specific Environmental Protection Agency fine or regulation the administration would use against San Francisco. But Trump said his administration would file some sort of complaint soon.

It’s not new for the president to use California as a left-wing punching bag to rile up his base, but his warning Wednesday night marked an escalation in his new intent to target the state’s homeless population. Even Fox News host Tucker Carlson has joined the offensive — he interviewed a business owner from San Francisco Wednesday night who said he was bitten by a homeless person.

Some California officials have long noted that local zoning regulations and fierce neighborhood opposition get in the way of less-expensive multi-family homes. Still, the state also welcomes federal intervention, especially more money to fix low-income housing and fewer attacks on programs that help lift people out of poverty, like Medicaid, food stamps, and public housing.

“We are focused on advancing solutions to meet the challenges on our streets, not throwing off ridiculous assertions as we board an airplane to leave the state,” San Francisco Mayor London Breed said in a statement Wednesday.

But Trump — who sent a delegation to Los Angeles’ Skid Row last week to observe the homelessness crisis firsthand — isn’t about to cough up anymore money for the solutions requested by Gov. Gavin Newsom and several mayors of California’s largest cities, represented by Sacramento Mayor Darrell Steinberg.

In a letter to California officials Wednesday, Carson — who also traveled to San Francisco this week — said the Trump administration had already done enough. He denied their requests for more federal rent vouchers and other housing aid. (The Trump administration has twice attempted to severely slash the nation’s affordable housing budget.)

“Federal taxpayers are clearly doing their part to help solve the crisis,” Carson wrote in the letter, according to Bloomberg News. “California cannot spend its way out of this problem using federal funds.”

In a White House report published earlier this week, Trump’s economic advisers also floated increasing support for police to crack down on street homelessness while also taking actions to slash housing regulations they think get in the way of more affordable units.