NATO summit will focus on increased defense spending, Ukraine support and growing threats from Russia's alliances with China, North Korea and Iran as President Donald Trump returns to the global stage.

Mr. Trump had been eager to celebrate his success at NATO and revel in the fact that he had conducted an attack that none of his predecessors had dared to launch. His view was backed up by Mark Rutte, the secretary general of the alliance, who wrote Mr. Trump a private message thanking him for his “decisive action” in Iran.