When President Donald Trump won the White House last year for the second time, many Democrats concluded they would need to moderate on a cluster of issues on which they were on the wrong side of public opinion. Chief among them was immigration, after nearly four years of willful neglect at the border had left the party’s reputation in tatters. On the day Trump returned to office in January, the Senate voted 64 to 35 to pass the Laken Riley Act. Named after a 22-year-old woman who was murdered by an illegal immigrant while she was jogging at the University of Georgia, the legislation stiffened penalties on illegal immigrants who commit crimes in the United States and mandated detention for more offenses. Twelve Democratic senators voted in the affirmative. Sens. Catherine Cortez Masto (D-NV), Jacky...