Outside the context of Mr. Trump’s two travel bans, few judicial rulings have addressed how much weight courts may put on statements from political candidates. Even informal remarks from sitting government officials are often ignored by courts, which can be reluctant to conduct what the Supreme Court has called “judicial psychoanalysis.”

But decisions about religious discrimination allow courts to consider government officials’ real purposes, even if their stated ones are neutral.

The Supreme Court has said judges may not turn a blind eye to the context in which government policies on religion arose. “Reasonable observers have reasonable memories,” Justice David H. Souter wrote in a leading religion case.
Justice Department lawyers had urged the judges to ignore Mr. Trump’s speeches on the campaign trail. “Candidates are not government actors, and statements of what they might attempt to achieve if elected, which are often simplified and imprecise, are not official acts,” the government said in a brief in the Maryland case. “They generally are made without the benefit of advice from an as-yet-unformed administration, and cannot bind elected officials who later conclude that a different course is warranted.”