President-elect Joe Biden promised to reverse a number of key immigration policies enacted under President Trump, raising fears of a surge at the southern border, which administration officials believe they already are seeing.

Biden has promised to end a number of Trump administration immigration policies, including many the administration said were key to ending “catch-and-release," a policy in which migrants are released into the U.S. while awaiting immigration hearings.

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Ending catch-and-release, in turn, discouraged migrants who headed north whether they had a valid asylum claim or not because they could be released into the country, according to some.

One of those policies was the Migrant Protection Protocols, known as the “Remain-in-Mexico” policy, which sent migrants to Mexico to await hearings. More than 60,000 migrants were enrolled in the protection protocols, many waiting just south of the border, a stone's throw from towns like Laredo, Texas, where immigration courts are set up. Very few ever are let in to the country.

Democrats and immigration activists said the policy is cruel, and forces migrants to wait in dangerous camps in Mexico where they can suffer violence at the hands of cartels and criminals. Biden promised to end it when he enters the White House.

That potential move raised fears of a surge at the border, with tens of thousands of migrants already there flooding through, followed by thousands more from Northern Triangle countries like Honduras, Guatemala and El Salvador.

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Acting Customs and Border Commissioner Mark Morgan, in a conference call with reporters on Thursday, said in response to a Fox News question, that it would be a disaster if protection protocols ended. Morgan was appointed by President Trump, but he also served as head of U.S. Border Patrol under President Obama.  

He said that in the 2019 fiscal year, CBP and Immigration and Customs Enforcement released more than 500,000 people into the United States. Since protection protocols expansion in mid-2019, that has plummeted, and in the 2020 fiscal year, 15,000 were released into the United States.

“If MPP is to go away it'll be absolutely devastating,” Morgan said,.

He called the calling the policy an “integral part of the network of policies that allowed us to end catch-and-release.”

Earlier in the call, Morgan announced that in October CBP encountered 69,000 immigrants entering the country without legal permission, an increase of 21 percent from September and a 54 percent increase from October 2019. 

Although this was before the Nov. 3 election, Morgan attributed it to “anticipated shifts in policy” that were creating new and widened pull factors, suggesting that the U.S. was already seeing signs of a possible border surge. He warned that it will only get worse if Trump policies are repealed.

“If you remove MPP as well as other policies that critics have said they're going to remove, make no mistake that is going to sound the alarm that our borders are open,” he warned.

It’s not the only policy Biden could scrap that might incentivize migrants to come north. He promised to end the Asylum Cooperative Agreements with Northern Triangle countries, which include demands that migrants claim asylum in those countries first. He also would impose a 100-day moratorium on deportations.

Biden promised to urge Congress to pass a “path to citizenship” for immigrants living in the the United States without legal permission.

Acting Homeland Security Secretary Chad Wolf also warned against overturning Trump policies, telling law enforcement at the border last month that "if these critical tools are removed or overturned, then the Department — and you, our frontline partners — would be imperiled by another immigration crisis."

"And, perhaps worst of all, you would be addressing this crisis with significantly less tools in your arsenal," he said.

Biden, however, has pledged to follow a plan to “build security and prosperity” in Central America, which he believes will solve the root causes of “irregular migration.”

“As president, Biden will immediately do away with the Trump administration’s draconian immigration policies and galvanize international action to address the poverty and insecurity driving migrants from the Northern Triangle to the United States,” his campaign website says.

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That includes a four-year, $4 billion regional strategy to address factors driving migration, to mobile private investment, improve security and rule of law, end corruption and prioritize poverty reduction and economic development.

The Biden transition team did not respond to a request for comment from Fox News.

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On Thursday, Morgan warned that the crisis that could follow a dramatic liberalization of laws and policies on illegal immigration and asylum could dwarf the 2019 border crisis during which more than 140,000 crossings occurred in a single month.

“The smugglers as we know, as history shows, as data proves, they will exploit the loopholes, and they will further exploit the migrants and you will see a crisis that makes last year's crisis look like child's play,” he said. “And you can take that to the bank.”