Technically, nobody knows what President-elect Donald Trump will do once he’s sworn into office.

But we do know what he promised to do, including withholding federal funding from 300 cities he feels do not cooperate with his proposed immigration policies—including San Francisco.

San Francisco’s sanctuary city policy limits the power of federal immigration agencies in city limits and limits the degree to which local government can work with federal law enforcement on immigration warrants for non-violent criminals.

(Note that there is no strict, legal definition of the term “sanctuary city,” and that seemingly unlikely burgs like Jackson Hole, Wyoming, and Anchorage, Alaska object to it.)

Mayor Ed Lee’s most recent budget proposal estimated that “federal grants and subventions in the general fund are budgeted at $251.9 million.”

Not that much relative to the city’s $9 billion budget, but still a number roughly equivalent to the amount the city spends on the homeless—and indeed, that’s where a lot of federal dollars go.

But the financial picture is more serious than that, because the city receives more funding than just those grants and subventions—including a lot of state funds that ultimately come from the federal government.

In all, it could add up to $915 million, as Supervisor Aaron Peskin told the San Francisco Examiner, much of it spent on the homeless, development, and infrastructure.

Although San Francisco has an enormous budget, only a fraction—as little as $20 million annually—is available for discretionary spending every year. That doesn’t leave a lot of wiggle room.

Mayor Lee says that the city’s immigration policies are not changing. Republicans in Congress have tried to punish San Francisco and other cities by cutting off funding before, but filibustering Democrats stymied the plan.