Defense Secretary Pete Hegseth was planning to head to Brussels last month to deliver what would be a bombshell announcement in a meeting with the North Atlantic Treaty Organization’s top military chiefs. The U.S., he planned to say, was preparing additional cuts to its forces in Europe that would go beyond the canceled deployment of an armored brigade to Poland and the earlier withdrawal of an infantry brigade from Romania, people familiar with the matter said. But Hegseth’s proposal was nixed after it was shared with Marco Rubio—President Trump’s national-security adviser—and other senior officials, the people said. Instead, Hegseth said...