Now, the Biden administration has announced it will start relieving the backlog starting February 19, with the Department of Homeland Security allowing about 300 people with active cases into the United States daily.
His administration suspended new entries into the program when he took office on January 20, but did not immediately put forward a plan to bring the people enrolled in it into the United States.
Trump administration officials said the border wall slowed down smugglers and people crossing the border illegally so they could be more easily apprehended.
White House Press Secretary Jen Psaki said on Wednesday: "now is not the time to come", adding that "the vast majority of people will be turned away". It also remains unclear how migrants will be tracked once they are admitted back into the U.S.
At the same time, the official said, Biden wanted to ensure they had the opportunity to have an open line of communication. Under the plan, migrants will need to register with global organisations over the Internet or by phone and await instructions. One of the organizations will also handle coronavirus testing in Mexico, another official said. Health officials in Los Angeles temporarily closed five vaccination centers Thursday, including a massive site at Dodger Stadium, after the city ran out of vaccine doses.
"When I was with Xi Jinping - and I was on the Tibetan plateau with him - and he asked me in a private dinner, he and I, and we each had an interpreter, he said, 'Can you define America for me?'" Biden recounted during a swearing-in ceremony for new staffers, hours after his inauguration.
Criticism of that administration's softly-softly approach to Beijing has intensified in recent years, with USA companies increasingly frustrated by what they say is state-sponsored industrial espionage, and fears over a lopsided trade relationship.
Even while Biden moves to end one Trump program, he faces growing pressure from advocates to end another known as Title 42. The U.N. migration agency's Mexico director, Dana Graber Ladek, said last month that it would seek to inform and support asylum-seekers on any changes in the "Remain in Mexico" policy.
Biden, who was then vice-president in the Obama administration, said he responded to Xi, who was then vice-president: "possibilities", CNN reported on Jan 22. "As more migrants catch wind of the reimplementation of 'catch-and-release, ' the surge on our border will be unimaginable".
Policies included efforts to build a border wall and separating children from thousands of migrant families.