The tiny Balkan nation of Montenegro, NATO’s newest member state, is suddenly in the news because of criticisms President Trump made of the alliance in a televised interview this week.

During the interview, with Tucker Carlson of Fox News, Mr. Trump turned his attention to Montenegro and raised questions about the United States’ commitment to the legal obligation that NATO members come to one another’s defense in the event of attack — a core commitment in the 1949 treaty that established the alliance.

When Mr. Carlson asked why, hypothetically, his son should be sent to Montenegro to defend the nation if it were attacked, Mr. Trump said he had “asked the same question” and went on to say the “aggressive people” of Montenegro could potentially start World War III.

(Mr. Carlson did not mention that the United States has an all-volunteer military; that there has not been a draft since 1973; or that the collective-defense clause of the treaty, known as Article 5, has been invoked only once in NATO’s history, after the Sept. 11, 2001, attacks on the United States.)