Tucked into President Trump’s 2018 budget request, in the form of language rewriting a 1996 law governing local cooperation with federal immigration enforcement, is a new front in the Trump administration’s war on “sanctuary cities” — jurisdictions that don’t help federal immigration agents scoop up unauthorized immigrants (and that happen, generally, to be under Democratic control).

The Trump administration is asking Congress to make it illegal for any law enforcement officer not to comply “with any lawful request” from federal immigration agents — including requests to hold immigrants after they’d normally be released from jail, so that federal agents can pick them up.

If the budget passed, it would put hundreds of cities that limit local help with federal agents — that say that, for example, local jails won’t hold immigrants booked on traffic offenses for Immigration and Customs Enforcement to pick up and deport — on the wrong side of the law.

The budget is extremely unlikely to pass. But it shows the White House is looking to Congress to intercede in a fight the Trump administration is currently losing.

After months of threats, the Trump administration finally admitted that it doesn’t currently have the ability to strip funds from cities like San Francisco and New York just because those cities don’t do everything they can to help the federal government round up unauthorized immigrants. But instead of surrendering, the administration wants Congress to change the law — and give it sweeping new powers to use against unauthorized immigrants, and against any city police department that tries to get in its way.

The law stands in the way of Trump’s agenda, so the administration wants to change the law

The Trump administration — especially Attorney General Jeff Sessions — has made a lot of noise about defunding “sanctuary cities” that don’t help the federal government enforce immigration law. But so far, its bark has been much worse than its bite.

That’s because of the ambiguity in what it really means to be a “sanctuary city.”

The Trump administration clearly wants to punish cities that don’t honor federal detainer requests — requests from federal agents to hold immigrants booked into local jails for 48 hours after they’d normally be released, to give the feds a chance to come pick them up and put them in deportation proceedings. That’s the sense in which it uses “sanctuary city” in its rhetoric, when it accuses cities like San Francisco and Chicago of abetting violent crime by shielding immigrants.

But right now it’s not illegal, under federal law, to decline a detainer request. So the only actions the Trump administration has taken so far target a definition of “sanctuary city” that’s so narrow that it’s not clear any city in America actually is one.

Federal law prohibits local and state governments from having policies that ban employees from sharing information with the federal government. The Trump administration has announced that it’s going to start withholding federal law enforcement grants from cities that violate the law by having such a policy.

Some cities do have policies on the books discouraging employees from sharing residents’ immigration status. And the Trump administration (following a report written under the Obama administration) has targeted a handful of them, asking them to certify they comply with the law. But the city governments maintain that they do — that they deliberately wrote their policies to comply with the federal law on information sharing.

The Trump administration clearly knows the information-sharing law isn’t broad enough to defund all the cities it wants to defund. It’s hinted that it’s going to define “sanctuary cities” more broadly in future — in other words, that it’s going to find a way to defund local governments for refusing to help federal agents pick up immigrants.

But even just hinting at that possibility was enough for a federal judge to force the Trump administration to put its “sanctuary city” defunding efforts on hold last month. The judge’s opinion made it clear that punishing cities for anything other than explicitly violating federal law wasn’t going to fly.

The Trump administration appears to finally be admitting that current law doesn’t allow it to do much on “sanctuary city” defunding. On Monday, a memo from Sessions clarified that the administration would only strip funding from jurisdictions that violated the federal information-sharing law.

And then on Tuesday, the budget’s general provisions contained language that would change the law itself — putting more cities in violation — and that would explicitly allow the Department of Homeland Security to prevent any city, state, or other government that violated such a law from getting DOJ or DHS grants.

The budget is a wish list — but now the wish has been made

If this proposal were to become law, the consequences could be huge. Hundreds of law enforcement agencies would be at risk of losing federal grants that many of them rely on for their budgets. It would put huge political strain on cities to start helping ICE pick up immigrants whenever asked.

And if those cities buckled — as many of them likely would — it would funnel hundreds of thousands more immigrants into federal deportation proceedings. Any encounter with law enforcement, even for the most minor offenses, would become a one-way ticket into the deportation process.

But the Trump administration is admitting that it can’t make this happen on its own. It’s asking Congress to change the law to make its policy possible. And it’s doing that by attaching the request to a 2018 budget that pretty much everyone in Congress, including Republicans, agrees is dead on arrival.

Congress is going to go its own way in enacting a budget for next year. It’s possible that it’s going to slip the language forcing cities to help federal immigration agents into the final budget, but it’s not hugely likely, because Congress doesn’t appear to be taking anything in the Trump budget terribly seriously.

The bigger concern for Democrats and city governments is that now that the legislative language has been written, Republicans in Congress could slip it in as a rider on a must-pass bill down the road — as a blow to (mostly Democratic-run) city governments, as a favor to the administration, or simply as an easy way to demonstrate they’re doing something on immigration.

If that happened, the Trump administration would finally be able to do what it’s been threatening to do all this time — and it would have the law on its side.