It was just days into his first term when President Trump issued an order banning the entry of people from several predominantly Muslim countries. An SOS went out to immigration lawyers across New York to head to Kennedy Airport, where arriving passengers were already being detained.

By noon, hundreds of lawyers were interviewing relatives and friends of travelers who were being held, challenging their detention and drafting petitions for their release.

The mobilization that morning in 2017 spawned a network of hundreds of lawyers who are now ready to fight the crackdown on immigrants that Mr. Trump promised to carry out in a second term in office.

After his decisive victory over Kamala Harris, Mr. Trump is expected to name key cabinet choices in the coming days and weeks, including his nominee to lead the Department of Homeland Security.

The Supreme Court upheld a version of the ban on travelers from several predominantly Muslim countries, which the Biden administration eliminated in 2021. But earlier this fall, Mr. Trump said he would “bring back the travel ban.”