Trump officials are encouraging conservative allies in Congress to prevent “sanctuary cities” from receiving federal funds as part of a spending bill that must pass next week to avoid another government shutdown.

The most conservative wing of the House Republican conference supports the idea of defunding these cities, which, as Vox’s Dara Lind explained, limit when they’ll help federal immigration agents detain unauthorized immigrants. This faction is open to the idea of getting it into the spending bill. With the White House’s backing, their resistance could pressure House Speaker Paul Ryan, even if he doesn’t want to inject additional controversy into the spending debate.

“We like that policy,” Rep. Jim Jordan (R-OH), who is part of the conservative House Freedom Caucus, said, confirming the White House’s efforts. “As the [spending bill] currently stands, no funding for the wall but there is funding for Planned Parenthood in it, and there is talk of putting insurance bailouts in it. And you think we are going to vote for that?”

Most congressional Republicans know that any bill that defunds sanctuary cities would be destined to fail in the Senate, where Republicans need Democrats to pass a bill. The language would make it nearly impossible to get anything to the president’s desk in the first place.

But time and again, President Trump has taken his cues from Congress’s archconservatives, and if he does again, this could escalate to another shutdown.

Trump wants to campaign on sanctuary cities

The White House has begun making both public and private calls to cut off federal funds for sanctuary cities, and the issue, which Republicans have used to rally their base, has been getting more attention as Trump hit the campaign trail last weekend.

“Today I am calling on Congress to stop funding sanctuary cities so we can save American lives,” Trump said at a rally Saturday in Pennsylvania. “The funding bill should not give precious and massive taxpayer grants to cities aiding and abetting criminals.”

Trump’s administration has amped up the confrontation over states and cities that try to offer additional protections to undocumented immigrants. The Department of Justice filed a lawsuit against California over three laws that limit government officials’ and employers’ ability to help federal immigration agents last week, and on Tuesday, Trump reiterated his desire to stop “sanctuary policies” over Twitter.

California’s sanctuary policies are illegal and unconstitutional and put the safety and security of our entire nation at risk. Thousands of dangerous & violent criminal aliens are released as a result of sanctuary policies, set free to prey on innocent Americans. THIS MUST STOP! — Donald J. Trump (@realDonaldTrump) March 13, 2018

So far, Trump’s call has excited those in the far-right wing of the caucus, who see this as an opportunity to claim a win on a spending bill that’s otherwise shaping up to be far less conservative than they’d like.

Immigration hawks have been railing against “sanctuary cities” for a long time. The definition has evolved. As Lind writes, “10 years ago, they were referring to something else: cities that didn’t inform the federal government when they had custody of an unauthorized immigrant.” Now a system finalized under the Obama administration connects immigration and FBI databases, so that nearly everyone booked into a jail gets run through both.

Republicans don’t seem to have much of an appetite for a fight over sanctuary cities

In the Senate, Republicans, while quick to chide sanctuary cities, don’t have an appetite to push the matter.

“There is widespread support for defunding sanctuary cities, and the Department of Justice has been vigorous in accomplishing that,” Sen. Ted Cruz (R-TX) told Vox. “What exactly is included in the omnibus at this point, I don’t know.”

Sen. James Lankford (R-OK), a member of the Senate Appropriations Committee in charge of putting together the spending bill, went further on the question.

“I doubt it [will be in the spending bill],” he said. “It’s still pressing through the courts right now. It’s also been something that our Democratic colleagues have been adamantly opposed to making any changes to sanctuary city policy.”

Senate Republicans put a bill that defunded sanctuary cities up for a vote early in February, during the chamber’s failed “open” debate on immigration policy. The bill, from Sen. Pat Toomey (R-PA), would have withheld non-law enforcement federal grant funds from so-called sanctuary cities. It failed 54 to 45, with almost all Democrats voting against it.

As lawmakers are working to pull together a more permanent spending bill by March 23 to keep the government open through the end of September, when the fiscal year ends, senators are being realistic.

Even Democrats don’t foresee a provision defunding sanctuary cities being slipped into the final spending measure.

“[Republicans] know they can’t do nasty stuff like that and get Democratic votes,” Sen. Brian Schatz (D-HI), who is also on the Appropriations Committee, said.

The government has already shut down twice this year, once directly over immigration policy in January when Democrats and some Republicans voted to shut down the government after a stalemate around the future of the Deferred Action for Childhood Arrivals program.

The second time the government shut down — for just a few hours overnight — in early February, it was because of a protest from conservative Sen. Rand Paul (R-KY), who was frustrated with a budget deal that has busted the government spending caps on domestic and military spending.

It all comes down to the White House

The White House hasn’t made clear how far it’s willing to take its calls for defunding sanctuary cities. For now, it’s been fodder for rally speeches and tweets. The White House did not respond to requests for comment.

But Trump made the issue a priority early in his presidency, signing an executive order to defund sanctuary jurisdiction that was ultimately blocked in the courts. As it stands now, the administration is escalating its efforts to prevent “sanctuary cities” from receiving federal grants and moving to stop states from passing laws that limit cooperation with federal immigration agents to begin with.

And in the past, Trump hasn’t been shy about raising the stakes to a government shutdown. In May 2017, he was reportedly talked out of vetoing the 2017 spending bill over a lack of border wall funding.

This spending bill is again shaping up to ignore Trump’s immigration priorities, and it’s possible the president could threaten a veto again.

He’s repeatedly called for a government shutdown as some kind of remedy for congressional gridlock, and while Republican and Democratic leaders in Congress have been rightfully wary of letting it get to this point again, Trump and his conservative allies seem willing to go that far.