U.S. representative Joaquin Castro, D–San Antonio, filed legislation on Friday aimed at heading off President Trump’s declaration of a national emergency so he can build a border wall—securing at least 226 cosponsors in the House and bringing the nation’s executive and legislative branches one step closer to a constitutional battle.

House Speaker Nancy Pelosi, who was in Laredo on Friday, told reporters that House Joint Resolution 46 would be on the floor for a vote Tuesday. Democrats now control that chamber after winning back the majority in the November midterms, so the resolution is assured of passage. But both lawmakers said they wanted the effort to be bipartisan to show that the legislative branch is opposed to the executive branch taking the “power of the purse” away.

So far, there is only one GOP member who is a cosponsor, representative Justin Amash, R-Michigan. The resolution would block Trump from acting by simply stating that the national emergency declared by the president “is hereby terminated.”

“What the president is attempting is an unconstitutional power grab,” said Castro, adding that such a move was “historic.” Trump decided to invoke emergency powers after he was rebuffed by a conference committee of House and Senate appropriators in getting $5.8 billion in funding for his signature campaign issue of a border wall. Trump cited a crisis at the border as the justification for circumventing Congress, which allocates federal funding under the Constitution. By declaring an emergency, Trump can go to other sources, such as the Pentagon, to get the funding necessary to build the wall.

But, said Castro, “There is no emergency at the border. Border crossings are at a decade low.” Castro took the lead on the issue six weeks ago when there were rumblings that Trump might declare a national emergency. The San Antonio Democrat, who is also the chairman of his brother Julián Castro’s presidential campaign, said, “There are big implications for military funding. My city, San Antonio, is known as Military City, USA.” He said that numerous projects around the state, including Joint Base San Antonio, Fort Bliss, and the Red River Depot, “could potentially be cut.”

It is a big moment in the spotlight for Castro, who has not been a particularly high-profile lawmaker since he was first elected to Congress in 2012. Pelosi, who also visited the Juárez–Lincoln International Bridge, in Laredo, told Castro how much she was relying on him. “You know the territory,” she said, as reporters listened. Pelosi credited Castro as being a leader among Texas Democrats knowledgeable about the border as the chairman of the Congressional Hispanic Caucus and with membership on both the House Intelligence Committee and the House Foreign Affairs Committee.

“Our privileged resolution will reassert our system of checks and balances,” said Pelosi.

The speaker also spent time Friday with U.S. representative Henry Cuellar, D-Laredo, a member of the appropriations committee, who was on the conference committee that came up with the compromise package on border security that fell short of what Trump wanted but prevented a second government shutdown is as many months. Pelosi emphasized that the process by which Congress decides how to spend the money has to be honored.

“This isn’t about politics. It’s not about partisanship. It’s about patriotism,” she said.

After the House vote, the resolution will move to the GOP-controlled Senate. A few Republicans are opposed to Trump’s use of emergency powers, though it is not clear how many would actually vote against him. Senator Ted Cruz has said he supported Trump using funds to build the border wall, and Senator John Cornyn, who is up for reelection, had initially indicated he was concerned about the emergency power declaration but in the last few days has been fund-raising off of Trump’s endorsement of him for reelection.

“President Trump is standing in defence [sic] of the millions of Texans placed at risk by a porous border, slowing the flow of drugs and crime into our neighborhoods,” Cornyn wrote supporters in a campaign email, asking them to sign a thank-you card to Trump. “By committing to a more secure border, the President shows us that he is dead serious about protecting Americans, and he needs to know that his efforts are appreciated.”

The House, at least, is expected to be delivering a very different message Tuesday.