(CNN) President-elect Donald Trump will face several significant hurdles if he attempts to quickly make good on a campaign promise to deport millions of undocumented immigrants from the United States, according to multiple immigration experts and law enforcement officials interviewed by CNN.
The likely obstacles to any mass deportation effort include required congressional approval for increased spending, vows of resistance by leaders in several major cities that are home to large numbers of potential deportees and long waits for removal proceedings in US immigration court.
"He's hamstrung," said Muzaffar Chishti of the Migration Policy Institute, a non-partisan Washington-based think tank. "He did not understand that we don't have a monarchy. We did not elect King Trump."
As Trump's inauguration approaches, there has been widespread handwringing among undocumented immigrants and their advocates as they wait to see how US immigration policy may change under a Trump administration. But there is mounting evidence that whatever actions he takes will not match the harsh rhetoric of the campaign trail.
What the immigration battle could look like under Trump
He's already waffled on his promise to build a wall, saying that existing fencing may suffice in some sections of the border. His controversial pledge of a temporary ban on all Muslims entering the US seems all but forgotten.
That leaves the deportation pledge.
"Mr. Trump will not be able or willing to engage in the kind of mass deportations that he promised in his campaign," said Stephen Legomsky, a professor emeritus at Washington University School of Law in St. Louis.
'More difficult than it sounds'
"Simply finding large numbers of undocumented immigrants with criminal records is much more difficult than it sounds," said Legomsky, who served as former chief counsel to US Citizenship and Immigration Services from 2011 to 2013 and as a senior counselor to Homeland Security Secretary Jeh Johnson in 2015.
Legomsky, who has since left government, said any such effort would be "incredibly laborious" and cost prohibitive.
In transition: President-elect Trump
President-elect Donald Trump shakes hands with Martin Luther King III
after they met at Trump Tower in New York on Monday, January 16. Afterward, King said the meeting was "constructive" and that the two discussed the importance of voting accessibility. Trump didn't speak to the media about the meeting.
Trump speaks at Trump Tower in New York on Wednesday, January 11. In
his first news conference since winning the election, a combative Trump made clear he will not mute his style when he is inaugurated on January 20. He lashed out at media and political foes alike.
US Sen. Jeff Sessions, Trump's nominee for attorney general, is sworn in during
his confirmation hearing in Washington on Tuesday, January 10. Trump and his transition team are in the process of filling high-level positions for the new administration.
Jared Kushner, Trump's son-in-law, arrives on Capitol Hill for a meeting with House Speaker Paul Ryan on Monday, January 9. Kushner, a 35-year-old businessman-turned-political strategist,
will be senior adviser to the president, a senior transition official told CNN.
Trump gets on an elevator after speaking with reporters at New York's Trump Tower on January 9.
Trump stands with Alibaba Executive Chairman Jack Ma, Asia's richest man, as they walk to speak with reporters at Trump Tower on January 9. Ma met with Trump to
tease plans for creating "one million" jobs in the United States. Trump praised Ma after the meeting as a "great, great entrepreneur and one of the best in the world."
Trump stands with legendary boxing promoter Don King after meeting at Trump's Mar-a-Lago resort in Palm Beach, Florida, on Wednesday, December 28. Trump and King
met to discuss the relationship between Israel and the United States.
Trump attends a meeting with Steve Bannon, chief White House strategist and senior counselor, at his Mar-a-Lago resort on Wednesday, December 21. Trump
spent the holidays in Mar-a-Lago.
Trump spokeswoman Kellyanne Conway talks to the press in the lobby of Trump Tower in New York on Thursday, December 15. Conway, who was Trump's campaign manager,
will work in his administration as "counselor to the president," it was announced on Thursday, December 22.
Trump
meets with technology executives in New York on Wednesday, December 14. From left are Jeff Bezos, chief executive officer of Amazon; Larry Page, chief executive officer of Google's parent company Alphabet; Sheryl Sandberg, chief operating officer of Facebook; and Vice President-elect Mike Pence. The three main areas discussed were jobs, immigration and China, according to a source briefed on the meeting.
Three of Trump's children -- from left, Donald Jr., Ivanka and Eric -- attend the meeting with tech leaders on December 14.
Trump, Pence and House Speaker Paul Ryan wave during an event in West Allis, Wisconsin, on Tuesday, December 13. "He's like a fine wine," Trump said of Ryan at
the rally, which was part of his "thank you" tour to states that helped him win the election. "Every day that goes by, I get to appreciate his genius more and more."
Trump and rapper Kanye West speak to the press after
meeting at Trump Tower in New York on December 13. Trump called West a "good man" and told journalists that they have been "friends for a long time." West later tweeted that he met with Trump to discuss "multicultural issues."
Trump
selected former Texas Gov. Rick Perry, right, to be his nominee for energy secretary, which would make Perry the head of an agency he once suggested he would eliminate.
Trump has tapped ExxonMobil CEO Rex Tillerson
to serve as secretary of state, the transition team announced December 13. Tillerson, seen here at a conference in 2015, has no formal foreign-policy experience, but he has built close relationships with many world leaders by closing massive deals across Eurasia and the Middle East on behalf of the world's largest energy company.
Trump waves during the Army-Navy football game, which was played in Baltimore on Saturday, December 10.
Trump shakes hands with Iowa Gov. Terry Branstad at an event in Des Moines, Iowa, on Thursday, December 8. Trump
re-introduced Branstad as his pick for US ambassador to China.
Trump greets retired Marine Gen. James Mattis at a rally in Fayetteville, North Carolina, on Tuesday, December 6. Trump said
he would nominate Mattis as his defense secretary.
Trump speaks to members of the media at Trump Tower in New York on December 6.
Trump visits the Carrier air-conditioning company in Indianapolis on Thursday, December 1.
Carrier announced that it had reached a deal with Trump and Vice President-elect Mike Pence, who is currently governor of Indiana, to keep about 1,000 of 1,400 jobs at its Indianapolis plant rather than move them to Mexico. The Carrier plant had been a theme of Trump's campaign promise to prevent more jobs from being outsourced to other countries.
Trump and former Massachusetts Gov. Mitt Romney
share a meal in New York on Tuesday, November 29. Romney was reportedly in the running for secretary of state.
Trump waves to a crowd at The New York Times building after meeting with some of the newspaper's reporters, editors and columnists on Tuesday, November 22.
Six takeaways from the meeting
Trump is flanked by Pence and Romney after a meeting in Bedminster Township, New Jersey, on Saturday, November 19.
"60 Minutes" correspondent Lesley Stahl
interviews Trump and his family at his New York home on Friday, November 11. It was Trump's first television interview since the election.
House Speaker Paul Ryan shows Trump and his wife, Melania, the Speaker's Balcony at the US Capitol on Thursday, November 10.
Trump walks with his wife and Senate Majority Leader Mitch McConnell after a meeting at the US Capitol on November 10.
Trump shakes hands with President Barack Obama following
a meeting in the Oval Office on November 10. Obama told his successor that he wanted him to succeed and would do everything he could to ensure a smooth transition.
Trump delivers his acceptance speech during his election night event at the New York Hilton Midtown hotel on Wednesday, November 9.
Early in the presidential campaign, Trump said all 11 million illegal immigrants in the US should be deported. He seemed to soften his stance after the election, telling CBS' "60 Minutes" that he would prioritize going after undocumented immigrants who had committed crimes beyond being in the country illegally.
The irony of that approach, experts say, is that it would be much easier for Trump to locate and begin deportation proceedings of non-criminals such as those granted temporary amnesty under President Barack Obama's Deferred Action For Childhood Arrivals Program.
The program, known as DACA, granted some 840,000 childhood-arrivals to the US temporary protection from deportation and issued them work permits. It was created by executive memorandum in 2012 and could be immediately rescinded by the Trump administration, stripping DACA participants of their protection against deportation.
California Dems tap Eric Holder to fight Trump in court
Going after undocumented immigrants with criminal records could prove more difficult and would likely require congressional approval to pay for more Immigration and Customs Enforcement agents to round up potential deportees who do not want to be found.
Key to that effort would be the cooperation of local law enforcement who run county jails and have the ability to alert ICE agents to the presence of undocumented immigrants with criminal records in their custody. Such inmates can be placed on an ICE "detainer" indicating that they are to be handed over to immigration officials when they finish their sentences. This could provide a steady flow of potential deportees without having to conduct costly and time-consuming searches.
But many big cities with large undocumented immigrant populations have said they would refuse to cooperate with such deportations under most circumstances. Some cities, including Los Angeles and Chicago, have set up legal defense funds for undocumented immigrants facing deportation.
Trump's threat
Trump has threatened to withhold federal funding from cities that don't cooperate with US immigration efforts -- an approach that could cripple local schools, police departments and airports, among others.
But Chishti predicted any such effort would face an immediate legal challenge. He said there were several Supreme Court cases that stood for the proposition that the federal government can't indiscriminately "hold a gun to the states' head."
A threat to withhold funds, he said, "must be in relation to the dispute at hand."
Even if officials were able to initiate a surge in deportation cases, such an effort would likely stall in immigration court where there is currently a backlog of more than a half million cases and a wait time of nearly two years.
Mark Krikorian, executive director of the Center For Immigration Studies, a non-partisan think tank in Washington, said Trump's campaign pledges to deport millions amounted to an "Archie Bunker moment" that should not have been taken seriously.
Who's in Trump's Cabinet?
"He's not going to be snapping his fingers and deporting millions of people over night," said Krikorain, whose group's motto is "Low-Immigration, pro-immigrant."
"That's not realistic," Krikorian said. "No one thinks that's going to happen."
But Krikorian said "it's very plausible" that Trump could ramp up deportations by 25% or more in 2017 and return to levels seen under Presidents Bill Clinton and George W. Bush, which he said reached about 400,000 a year when Bush left office.
That, he said, could be done without significant budgetary increases and despite resistance from sanctuary cities.
"I think the other side is making it seem more complicated than it needs to be," he said.
Stephen Yale-Loehr, who teaches immigration law at Cornell Law School, agreed that Trump would be able to have meaningful impact during the first year of his presidency, but not to the extent suggested during the campaign.
"On the campaign trail things are not nuanced. They're black and white," Yale-Loehr said. "It takes a while to turn the battleship of bureaucracy around."