Immigration advocacy groups and Democratic leaders are seeking to disrupt the president-elect Donald Trumphis plan to deport millions of undocumented immigrants through lawsuits that could be filed as soon as he takes office.

Trump has vowed to carry out what he calls the “largest deportation operation” in the country’s history and has pledged to reinstate and expand the controversial ban on people coming to the US from certain Muslim-majority countries as part of his immigration policy.

On Monday, he reiterated on Truth Social that he is prepared to declare a national emergency and use military means to fulfill his promise of mass deportation.

Several immigration advocates and Democratic leaders told ABC News they have spent months preparing for the prospect of a new Trump presidency and the expected crackdown on immigrants that Trump and his new border czar Tom Homan have promised

Homan, who embraced Trump’s pledge to carry out mass deportations on “Day 1” of the new administration, oversaw US Immigration and Customs Enforcement (ICE) during the Trump administration’s “zero tolerance” enforcement, which separated parents of their children at the border. .

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“In California, we’ve been thinking about the possibility of this day for months, and in some cases years, and we’ve been preparing and preparing by looking at all the actions that Trump has said he’s going to take,” the prosecutor said. California Gen. Rob Bonta. ABC News.

Bonta said his team prepared briefs on several immigration issues that Trump mentioned during the campaign. including mass deportations, birthright citizenship, Deferred Action for Childhood Arrivals (DACA), and sanctuary cities.

“There will be pain and harm caused by him. Not everything is avoidable, but to get into our immigrant communities in ways that break the law, they’re going to have to go through me and we’re going to stop them. in the courts, using the legal tools they gave us,” said Bonta.

California’s attorney general says 80 percent of the state’s legal challenges to Trump’s first-term executive orders and immigration policies have been successful.

“We’re very confident that we’re going to block the major efforts of the federal administration and that we’re going to be able to kill some of the worst ones,” Bonta said.

The 24 Democratic state attorneys general in the United States hope to present a united front to block the Trump administration’s immigration policy, using his first term as a model, according to Sean Rankin, president of the Democratic Attorneys General Association.

“When we look at immigration, we know this is something that the president has talked about over and over and over again,” Rankin told ABC News. “Right now, we’re not connecting the dots. Follow flashing arrows. It’s very easy to see where they will end up.”

One of Homan’s targets in his mass deportation plan are sanctuary states and cities — places that have enacted laws designed to protect undocumented immigrants. The policies, which vary by state, generally prohibit city officials from cooperating with federal immigration authorities.

“They better get the hell out of the way,” Homan said last week, referring to sanctuary state governors. “Either you help us or get the hell out of the way, because ICE is going to do their job.”

Leaders in several sanctuary cities have said they will fight back using all legally available tools to protect communities from immigrants.

“We’ve worked in this office to prepare for a lot of different scenarios, and we’re going to be prepared to deal with them with all the tools that we have,” Washington Attorney General Bob Ferguson said at a press conference last week .

Ferguson told reporters that between 2017 and 2021, his legal team defeated 55 “illegal actions” and policies from the Trump administration. But while his office has been preparing litigation for months, Ferguson said he believes the second Trump administration will also be better prepared than the first.

“One of the many reasons we were successful with our litigation against the Trump administration was that they were often sloppy in the way they went about it, and that gave us openings to prevail,” Ferguson told reporters. “In court this time, I anticipate we’ll see less of that, and that’s an important difference.”

In addition to considering using the military to carry out deportations, Trump and his allies have suggested using an obscure section of the Alien and War Acts of 1798 — a set of 18th-century wartime laws — to immediately deport some migrants without a hearing. .

Lee Gelernt, deputy director of the American Civil Liberties Union’s Immigrant Rights Project, told ABC News that they were preparing for the potential use of the military to carry out deportations.

“They’re going to try to use the military, under the alien enemies act, to deport people summarily,” Gelernt said. “We’ll try to challenge her right away.”

Gelernt, who led the ACLU’s legal response to family separations in Trump’s first term, said he expects the next Trump administration to be “worse for immigrants” than the first.

“It seems that the Trump team has been preparing for four years to implement anti-immigrant policies, and the rhetoric in the country has become much more polarized than it was in 2016,” Gelernt said.

During Trump’s first term, Gelernt said groups like the ACLU were caught off guard with some of his executive orders, such as the travel ban — but this time, the organization has been preparing litigation for nearly a year. In 2018, the Supreme Court upheld Trump’s controversial travel ban from several predominantly Muslim countries, which the Biden administration later removed. Since then, Trump has appointed two justices to the Supreme Court.

“We plan our challenges with much more advanced training and do our best to coordinate between the various NGOs (non-governmental organizations) in the country,” Gelernt said.

“As litigants, we’ve come together, we’ve prepared, we’ve tried to anticipate the unimaginable as we move into the next four years,” said Alina Das, co-director of the Immigrant Rights Clinic at New. York University School of Law.