Speaking before a joint session of Congress on Wednesday, NATO Secretary-General Jens Stoltenberg had a message for Washington: allies matter, and they're good for the U.S.

Congress answered his remarks with applause and standing ovations. But as NATO faces new threats, lawmakers must do more than clap.

This month marks NATO's 70th anniversary. The alliance has not only aged but also evolved, and it remains as relevant as ever. But it also faces new threats, including a lack of American leadership, as made clear by a report from Harvard's Belfer Center. As the report bluntly puts it: “Most significant is a challenge NATO has not faced before: the absence of strong American presidential leadership.”

Concerns about U.S. support for the alliance were clearly on display on Wednesday during Stoltenberg's address to Congress. Indeed, his speech seemed to dwell on the seemingly obvious point that the U.S. benefits from NATO.

As Stoltenberg explained, “The strength of a nation is not only measured by the size of its economy or the number of its soldiers, but also by the number of its friends. And through NATO, the United States has more friends and allies than any other power.”

At the Capitol, this appeal to lawmakers was met with standing ovations and applause. Lawmakers heard what Stoltenberg was saying and clearly showed their agreement. But they need to do more, because the White House still seems bent on undermining NATO.

President Trump’s has repeatedly questioned U.S. commitments to uphold mutual defense agreement under Article 5. He has used NATO meetings to berate allies based on his flawed understanding of NATO spending targets. He has picked unnecessary fights over trade with key allies. And more recently, his administration has proposed pulling funds for defense projects against Russian aggression to fund an unneeded border wall. These actions not only threaten to undermine the success of a safe, peaceful and secure Atlantic that NATO has fostered, but also signal a lack of U.S. commitment to the alliance that emboldens the very aggression it was designed to counter.

On Wednesday, Congress made a point of standing up for NATO. In practice, lawmakers must make clear that they don't support Trump's devil-may-care approach to the alliance.