The U.S. Supreme Court June 21 made it a little easier for longtime U.S. residents facing removal to stay in the country with their families.

But the 8-1 decision prompted a short but eyebrow-raising concurrence from Justice Anthony M. Kennedy, calling into question the deference courts give administrative agencies under the Supreme Court’s 1984 decision in Chevron U. S. A. Inc. v. Natural Res. Def. Council, Inc. Under Chevron, courts need to defer to reasonable agency interpretations of...