In a bold move, President Donald Trump has announced plans to withhold federal funding from states that house local governments defying his immigration policies. This decision, set to take effect from February 1, signifies an expansion of his earlier threats to cut resources to sanctuary cities—jurisdictions that limit cooperation with federal immigration enforcement.

This proposed action could potentially ripple across the nation, impacting even regions not particularly noted for their hospitality toward noncitizens. The implications are vast, as federal funding often supports a wide array of state-level programs and services.

Trump’s previous attempts to sever funding for sanctuary jurisdictions faced legal hurdles, with courts blocking those efforts. Despite this, he reintroduced the idea during a speech at the Detroit Economic Club, though specifics remained largely unaddressed.

“Starting Feb. 1, we’re not making any payments to sanctuary cities or states having sanctuary cities,” Trump declared. He argued that these jurisdictions protect criminals at the expense of American citizens, leading to increased fraud and crime.

When pressed by reporters in Washington for details on which funds would be affected, Trump remained vague, simply stating, “You’ll see. It’ll be significant.” This leaves many wondering about the potential scope and impact of the funding cuts.

Back in Washington, Trump was asked by reporters what kind of funding would be affected on Feb 1: “You’ll see,” he said. “It’ll be significant.”

There is no strict definition for sanctuary policies or sanctuary cities, but the terms generally describe limited cooperation with Immigration and Customs Enforcement.

Courts have rejected the idea before

In an executive orders last year, the president directed federal officials to withhold money from sanctuary jurisdictions that seek to shield people in the country illegally from deportation.

A California-based federal judge struck it down despite government lawyers saying it was too early to stop the plan when no action had been taken and no specific conditions had been laid out.

In Trump’s first term in office, in 2017, courts struck down his effort to cut funding to the cities.

Some of the details are tricky

The Justice Department last year published a list of three dozen states, cities and counties that it considers to be sanctuary jurisdictions.

The list is overwhelmingly made up of places where the governments are controlled by Democrats, including the states of California, Connecticut and New York, cities such as Boston and New York and counties including Baltimore County, Maryland, and Cook County, Illinois.

That list replaced an earlier, longer one that was met with pushback from officials who said it wasn’t clear why their jurisdictions were on it.

The administration has been threatening funding in specific places

The federal government has moved to halt funding for a variety of programs in recent weeks and is already facing legal challenges.

The U.S. Department of Agriculture has warned states that have refused to provide data on recipients of Supplemental Nutrition Assistance Program money that they’ll be docked administrative funds. A court fight over the request for information was already under way before the threat came. Money hasn’t been stopped yet.

The U.S. Department of Health and Social Services said last week that it was halting money from five Democratic-led states for daycare subsidies and other aid to low-income families with children over unspecified suspicions about fraud. A court put that on hold

The administration has tried to use additional financial pressure against Minnesota, a state where it has also sent a wave of federal officers in an immigration crackdown. The Agriculture Department has said it’s freezing funding in the state — but without laying out many details.

The Centers for Medicare and Medicaid Services also told Minnesota last week that it intends to withhold $515 million every three months from 14 Medicaid programs that were deemed “high risk” after rejecting a corrective action plan it demanded because of fraud allegations. The amount is equivalent to one-fourth of the federal money for those programs. State officials said Tuesday that they’re appealing.