On Tuesday, President Trump announced a new policy set to take effect on February 1, which will block federal funds to states harboring local governments that oppose his administration’s immigration protocols. This move builds on his previous warnings to withhold resources from so-called sanctuary cities.

This decision could have a broad impact across the nation, potentially affecting even those areas that are not particularly supportive of noncitizens.

Trump’s earlier attempts to cut funding to sanctuary jurisdictions were thwarted by judicial rulings.

During a speech at the Detroit Economic Club, Trump introduced this latest plan but did not provide further details.

“Starting Feb. 1, we’re not making any payments to sanctuary cities or states having sanctuary cities, because they do everything possible to protect criminals at the expense of American citizens and it breeds fraud and crime and all of the other problems that come,” he said. “So we’re not making any payment to anybody that supports sanctuary cities.”

When questioned in Washington about which funds would be targeted starting February 1, Trump responded, “You’ll see. It’ll be significant.”

The term sanctuary city lacks a precise definition, generally referring to jurisdictions that limit their cooperation with Immigration and Customs Enforcement.

Courts have rejected the idea before

In an executive order 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 New York, California and Connecticut, and counties such as Baltimore County, Md., and San Diego County, Calif. The New York cities on the list include NYC and Rochester, while New Jersey is home to four — the most sanctuary cities of any state — Newark, Jersey City, Hoboken and Paterson.

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 Department of Agriculture has warned states that have refused to provide data on recipients of money from the Supplemental Nutrition Assistance Program 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 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.