President Trump’s efforts to tighten U.S. asylum laws through an executive memorandum represents the latest acknowledgment from the White House that his proposed border wall will do little to stem a record surge of migrant families.

Administration officials offered few new details Tuesday about the president’s order to the Department of Homeland Security and the Justice Department to develop regulatory proposals within 90 days aimed at restricting the rights of asylum seekers and speeding up a backlog of immigration court hearings.

But privately, current and former Trump aides described the move as the culmination of a year-long campaign by senior White House adviser Stephen Miller to force the administration’s hand. Miller has argued that restricting asylum would prove more effective than alternative border control measures to reverse the spike in migrant families from Central America, according to two former administration officials who worked closely with him.

People with knowledge of the internal deliberations said Trump’s decision three weeks ago to change DHS leadership — replacing Secretary Kirstjen Nielsen with longtime DHS immigration official Kevin McAleenan — was made in part over concerns at the White House that agency officials were undermining the president’s immigration agenda by failing to draft asylum changes.

Miller has rebuked agency officials for not complying with requests from the White House, said a former administration official, who described him as “obsessed” with the asylum issue. Miller has persuaded the president that many of the people seeking asylum do not qualify for such protections, said the former official, who spoke on the condition of anonymity to describe private conversations.

During a speech at the National Rifle Association convention in Indianapolis last week, Trump pledged to follow through on his efforts to build a border wall, but he suggested that changing immigration laws would be more effective.

“The wall is one thing, and that will have an incredible impact,” Trump said, but the migrants “won’t even be coming up if we change our old, broken, ridiculous, weak immigration laws.”

Miller declined an email request for comment. A DHS spokesman did not reply to an additional request.

In his memo released late Monday, Trump stated that the administration would seek rules to charge asylum seekers fees and block them from receiving work permits as they await court hearings, while requiring that immigration judges rule on cases within 180 days.

Yet White House allies and critics alike predicted that the changes would face legal challenges once they are unveiled, and they expressed doubt over the impact even if the rules are adopted after what could be a lengthy public process.

“There’s a limit to what regulation is going to be able to do,” said Mark Krikorian, executive director of the Center for Immigration Studies, which advocates for lower immigration levels. “I just don’t see how this can be dealt with short of legislative changes.”

Even as the president has demanded billions of dollars in funding for a border wall, his administration has more quietly pressed Congress to end a system that officials call “catch-and-release.” Under U.S. law, Central American families with children cannot be detained for more than 20 days, and unauthorized migrants are generally released into the United States while awaiting their asylum hearings, which can take more than a year because of court backlogs.

But Democrats, and some Republicans, have called the administration’s legislative proposals a non-starter, prompting the White House to pursue unilateral action. Last fall, a federal judge blocked a Trump order that aimed to ban Central Americans who cross into the United States between legal ports of entry from applying for asylum protections.

Theresa C. Brown, who served as a DHS policy official under Presidents George W. Bush and Barack Obama, said that Trump’s memo appeared to be a more well-considered effort to make changes.

“If you compare this to proclamations earlier in his presidency, this represents a lot more thought from people who understand the process operationally and regulatorily,” Brown said. But she added that it was unclear whether Trump was seeking to expedite rule changes under the national emergency he invoked at the border in February or pursue the more traditional path of allowing public input on proposed rule changes, a process that could stretch well into next year.

Democrats blasted the White House plan and called on Trump to support more funding for humanitarian programs in Central America that seek to address the problems causing migrants to leave home for the United States.

“This despicable attack on desperate families seeking asylum is cruel, unprecedented and fails to address the root causes of migration,” House Speaker Nancy Pelosi (D-Calif.) said in a statement Tuesday. “This inhumane action is a stark departure from past presidents, Republican and Democrat, who have always recognized that the lifeline of asylum is central to our nation’s values, history and future.”

The number of migrants apprehended at the southern border rose to 103,000 in March, the highest level in more than a decade. Testifying before a House subcommittee on Tuesday, McAleenan said that 5,000 migrants were apprehended on April 16, and he added: “Simply put, the system is full, and we are well beyond our capacity.”

In an interview with the Daily Caller on April 2, Miller said the White House was pursuing an “aggressive effort to utilize every existing authority in statute” to stem the flow. Five days later, Trump pushed out Nielsen and elevated McAleenan, who had been serving as commissioner of Customs and Border Protection. Trump told reporters he wanted to go in a “tougher direction.”

But former government officials criticized the Trump administration as pursuing quick-fix policies that have worsened the problem at the border. Cecilia Muñoz, who served as White House domestic policy adviser under Obama, said human smugglers use Trump’s threats to tighten border controls as an incentive for migrants to make the trip before entry becomes more difficult.

“The bigger mistake the administration is making is assuming you can fix what’s happening at the border just with the tools available in the United States,” Muñoz said. “If you just try to shut down the asylum system as much as possible and think magically that immigration will stop, that’s not how migration works.”