Then came potshots at Germany’s chancellor, Angela Merkel, a strong leader who is facing a tough re-election. He called her brave decision to open Germany’s borders to migrants and refugees a “very catastrophic mistake.” He also suggested that he saw no difference between Ms. Merkel and Vladimir Putin, saying he would, at least initially, trust them equally, even though it was the Russian president who meddled with the American election, bombed civilians in Syria, crushed dissent in his own country and invaded Ukraine.

It is puzzling indeed for a president-elect to publicly denigrate leaders of his country’s closest allies as well as an alliance that for 70 years has stood firm against Russian expansion. And Mr. Trump’s criticism of NATO’s response to terrorism showed no awareness of the alliance’s contributions to the fight against the Taliban and Al Qaeda in Afghanistan and the Middle East.

Mr. Trump did say during the interview that “NATO is very important to me,” but in the context of his other remarks, this was hardly enough to blunt the impression that he placed little value on NATO’s historic role as a defender of democracy and its continued usefulness today. Nor did Mr. Trump’s remarks ease concerns that his choices for cabinet members, some of whom seem to have a much firmer grasp of foreign policy than he does, will have little if any influence on administration policy. During their recent confirmation hearings, Rex Tillerson, the nominee for secretary of state, said he saw value in durable alliances; retired Gen. James Mattis, the defense secretary designate, went even further, asserting that “if we did not have NATO today, we would need to create it.”

Mr. Trump’s comments on the European Union almost took the breath away: “I don’t think it matters much for the United States.” The union has its problems, as Britain’s vote to leave it has shown, but to cavalierly dismiss as unimportant the idea of European integration and the second-largest market in the world is to ignore history and reject the future. Mr. Trump seems eager to help unravel the rules-based international order.

The big winner in all this is Mr. Putin, who has been working assiduously not just to delegitimize American democracy by interfering with the election but to destabilize Europe and weaken if not destroy NATO, which he blames for the Soviet Union’s collapse. Mr. Putin will almost certainly try to persuade Mr. Trump to withdraw American support for NATO’s plans to reinforce its defenses against a newly assertive Russia. As part of that effort, an American convoy crossed into Poland last week; on Monday, the deployment of 330 American Marines to Norway began. Reversing course any time soon would be a huge mistake.