President Trump’s immigration-enforcement tactics have been defined by a muscular use of executive power with little precedent. Now, a federal judge is tasked with deciding whether to curtail that approach against foreigners in the U.S. legally. U.S. District Judge William Young in Boston wrapped up a closely watched trial this week on the administration’s targeting of international students engaged in campus activism. Following a series of high-profile arrests of pro-Palestinian protesters, faculty groups are pressing a broad legal effort to head off similar future arrests. The litigation taps into rarely explored legal tensions between the government’s latitude to set the...