CHANGE: Donald Trump Sets Conditions for Defending NATO Allies Against Attack.

During a 45-minute conversation, he explicitly raised new questions about his commitment to automatically defend NATO allies if they are attacked, saying he would first look at their contributions to the alliance. Mr. Trump re-emphasized the hard-line nationalist approach that has marked his improbable candidacy, describing how he would force allies to shoulder defense costs that the United States has borne for decades, cancel longstanding treaties he views as unfavorable, and redefine what it means to be a partner of the United States.

He said the rest of the world would learn to adjust to his approach. “I would prefer to be able to continue” existing agreements, he said, but only if allies stopped taking advantage of what he called an era of American largess that was no longer affordable.

Article 5 of the North Atlantic Treaty says that “an armed attack against one or more of them in Europe or North America shall be considered an attack against them all.” It has been invoked only once in NATO’s 67-year history, in defense of this country after the attacks on Washington and New York City of 9/11/2001.