Jim Mattis, as secretary of defense, has done his best to preserve and defend the system of global alliances that the United States spent the last 70 years building and leading. In his resignation letter on Thursday, Mr. Mattis wrote that the United States was the “indispensable nation in the free world.”

“Our strength as a nation,” he wrote, “is inextricably linked to the strength of our unique and comprehensive system of alliances and partnerships.”

That’s apparently not the view held by President Trump, who ran for office calling for America to do less, calling for our allies to spend more and inviting rival nations to be more assertive.

Some people thought that once Mr. Trump was in office and had shouldered presidential responsibilities, he would adopt a less knee-jerk view of how best to keep the nation safe and the free world free.