Alan Gomez

USA TODAY

So how big will Donald Trump's wall really be?

The wall along the southwest border with Mexico was one of the president-elect's signature campaign promises, as he railed against illegal immigration and vowed to seal the borders against criminals, terrorists and millions of people trying to enter the United States legally. Now, immigration experts are trying to figure out exactly how those policies will work in a Trump administration.

And so far, it looks like he will be able to follow through on many of his pledges — with or without help from Congress.

"Generally speaking, any president has wide discretion when it comes to enforcing our immigration laws because immigration touches on national sovereignty," said Stephen Yale-Loehr, a professor at Cornell Law School and author of a 21-volume treatise, Immigration Law and Procedure.

MORE DEPORTATIONS

The first, and possibly easiest, change Trump can make is redirecting the Department of Homeland Security to ramp up deportations. At the beginning of the campaign, Trump said all 11 million undocumented immigrants in the country must go. In the closing months, he talked more about deporting immigrants with criminal records — "bad hombres" — and opened the possibility of finding a way for some to remain in the country.

In an interview that aired Sunday on CBS' 60 Minutes, Trump said he plans to immediately deport 2 million to 3 million undocumented immigrants. Trump said he would emphasize criminals before deciding about law-abiding families illegally in the country.

Trump would need congressional approval to hire more Border Patrol agents to monitor the frontier and Immigration and Customs Enforcement agents to round up immigrants living in the interior of the country. Trump doesn't need any new money to change the focus of the immigration agents who are already in place, said Ali Noorani, executive director of the National Immigration Forum, an immigrant advocacy group.

"If the Department of Homeland Security secretary greenlights, simply in tone, the ramping up of enforcement actions, that is a system that can wreak havoc very, very quickly," Noorani said.

DACA recipients fear Trump will force them back into the shadows

ENDING DEPORTATION PROTECTIONS

Trump could unilaterally revoke the deportation protections President Obama created under the Deferred Action for Childhood Arrivals program, known as DACA. More than 840,000 young undocumented immigrants have been approved for that program, which protects them from deportation for two-year periods and grants them work permits.

Stephen Legomsky, professor emeritus at Washington University School of Law in St. Louis and a former chief counsel at U.S. Citizenship and Immigration Services, said Trump could revoke every single DACA case very simply. The program was created by an executive memorandum by Obama's secretary of Homeland Security, and President-elect Trump's secretary could simply rescind that memo or issue a new one.

It would be more complicated to revoke their work permits. Under U.S. law, Homeland Security must provide written notice that it plans to revoke the permits and recipients have 15 days to respond — but don't have a right to a court hearing to fight the revocation.

Legomsky questioned whether Trump would then move to deport all those DACA recipients. Since Trump won't be able to quickly deport all of the nation's undocumented immigrants, Legomsky said DACA recipients are the least likely targets since they have clean criminal records, they've been working or going to school and they've already been vetted by the federal government.

"As a practical matter, it seems like these folks would be the lowest priority of all," he said.

ENDING REFUGEE PROGRAMS

A president has very broad, unilateral discretion to determine which refugees — those fleeing war and other threats to their safety — are admitted into the country.

The number of refugees accepted by the U.S. each year is set exclusively by the president. President Obama has increased the number of refugees from 70,000 in 2015 to 110,000 in 2017. Trump repeatedly bashed that decision, saying refugees from countries like Syria were threats to national security because they had not been properly vetted and could include terrorists. The State Department says Syrian refugees undergo the strictest background checks.

As president, Trump could drop the total number of refugees to zero.

"Congress can ask questions and object to things, but ultimately it's up to the president," Legomsky said.

Donald Trump's call for banning Muslims from entering U.S. draws condemnation

THE MUSLIM BAN

Presidents have the power to bar access to the U.S. to specific immigrants or entire classes of immigrants. That power is laid out in the Immigration and Nationality Act, which allows a president to block would-be immigrants if they are deemed "detrimental to the interests of the United States."

Yale-Loehr said that provision has been used sporadically over the decades to bar dictators, military strongmen and others who worked to undermine democracy in countries like North Korea, Venezuela, South Sudan and Libya. But he said it’s never been used in the way or the extent proposed by Trump, who had initially called for a temporary ban on all immigrants from all Muslim countries.

Such a proposal would have likely faced a slew of lawsuits from groups claiming it violates First Amendment protections for freedom of religion. In recent months, Trump altered the description of his ban, saying he would target immigrants from “terror-prone regions where vetting cannot safely occur.”

Legomsky said if Trump worded such a proclamation based on terrorism grounds and not on religious grounds, "then I'm sure that order would hold up in court."

Border towns to Trump: The wall won't work

THE BORDER WALL

Extending the 650 miles of wall or fencing that currently exist would require congressional approval because of the billions of dollars that the project would cost. Trump told 60 Minutes that in "certain areas, a wall is more appropriate," but "there could be some fencing."

Congress may need to create a legal mechanism to withhold remittances that Mexicans in the U.S. send back to their families in Mexico, a revenue stream that Trump says would help pay for construction of the wall.

So far, it looks like there's interest on Capitol Hill. Senate Majority Leader Mitch McConnell, R-Ky., said on Wednesday that border security "is something I think ought to be high on the list." And House Speaker Paul Ryan, R-Wis., said Trump has earned a "mandate" to implement his policy.

But Tuesday's election left Republicans short of the 60-vote majority in the Senate that would allow them to override a Democratic filibuster that could block legislation, meaning Republicans may need to craft a compromise to get the wall extended.

Rep. Mario Diaz-Balart, R-Fla., one of the lead immigration negotiators in the House, said he would be willing to accept extensions to the border wall as long as part of the package includes legal protections for undocumented immigrants who remain in the U.S.

"The size of a wall, the thickness of a wall, the size of a fence — whatever it takes to finally secure the border — I think Congress will have the willingness to do that," Diaz-Balart said. "But in order to do all of that, you're going to have to get it through the Senate. The mathematical reality of that is you're going to have to deal with the (undocumented immigrants) who are here."