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A growing number of law enforcement authorities and Democratic leaders across the country are speaking out about their plans to thwart one of President-elect Donald Trump’s top immigration priorities: Mass deportation. Taking lessons from the first four years of the Trump era, many have vowed to stand their ground and refuse to cooperate with federal law enforcement in arresting undocumented immigrants. They are also preparing counter-lawsuits to have ready to take the incoming administration to court as soon as officials attempt to begin deportations, which they’ve promised to kick off on day one.

In interviews with Politico published Saturday, prosecutors in six Democratic-led states described their plans to pursue legal challenges against actions Trump may take to carry out his immigration agenda.

These include the potential deployment of the US military domestically to find undocumented people, violations of immigrants’ rights to due process, the withholding of funds from s0-called sanctuary cities, and attempts to deputize the National Guard from red states to carry out arrests and detentions in blue ones.

These prosecutors said they’re also preparing to fight scenarios where the administration tries to send immigration agents into schools and hospitals, or where they withhold federal funds from local law enforcement to force them into compliance with deportation plans.

Earlier this week, Trump reaffirmed his plans to declare a national emergency in order to use federal troops to round-up targets for deportation.

“If he’s going to want to achieve that type of scale, the largest deportation in US history, as he says, by definition he’s going to have to target people who are lawfully here and … go after American citizens,” Matthew Platkin, New Jersey’s attorney general told Politico, likely referring to the fact that millions of undocumented people live with US citizens, including those whose children were born on American soil. Those children would have to leave the country with deported parents in order for families to stay together. “We’re not going to stand for that,” Platkin added. The goal of top prosecutors across blue states, the president of the Democratic Attorneys General Association Sean Rankin told ABC News, is to put up a “unified front” against Trump’s immigration agenda.

The Trump administration will inevitably face not only legal but logistical obstacles if they attempt to deliver on the promise of conducting an unprecedented mass deportation campaign. As Dara Lind with the American Immigration Council recently wrote in the New York Times, deporting one million undocumented immigrants per year—a fraction of the estimated 11 million living in the country—would cost an annual $88 billion. The limited number of detention beds and immigration courts’ years-long backlog will also inhibit a massive crackdown.

Still, Tom Homan, Trump’s new “border czar,” who won’t require Senate confirmation, has indicated the administration will push hard against jurisdictions that get in their way. “If we can’t get assistance from New York City,” Homan told Fox News recently, “we may have to double the number of agents we send to New York City. Because we’re going to do the job. We’re going to do the job without you or with you.” And in fact, Homan has a history of pushing forward extreme immigration policies: As a US Immigration and Customs Enforcement (ICE) official during Trump’s first term, he was the architect of the “zero tolerance” policy that separated thousands of parents from their children at the border. To this day, many have not been reunited.

Several Democratic leaders have publicly said they won’t go along with mass deportation efforts. Massachusetts Gov. Maura Healey, who sued the Trump administration 100 times as attorney general, said they would use “every tool in the toolbox” to protect the state’s population. In a statement, a spokesperson for the Rhode Island State Police said while they cooperate with ICE, “they are not immigration officers and will not expend any time and resources to support mass deportation efforts.”