Should the U.S. rethink its commitments to NATO?

President Trump criticized NATO while on the campaign trail because he felt NATO allies were not fairly sharing the burden. Trump thinks it's a bad deal for the U.S. to shoulder the bulk of military spending so the European Union can kick back and not worry about their own defense.

In one important way, the defense secretary amplified the president’s previous statements. Though Mr. Mattis acknowledged “concern in European capitals about America’s commitment to NATO and the security of Europe,” he said allies must do more to reach their commitments to spend 2 percent of gross domestic product on defense. “No longer can the American taxpayer carry a disproportionate share of the defense of western values,” he said.

Trump sees NATO as an obsolete institution that fails to address the biggest threat today—radical Islamic terror.

But many officials here remained unconvinced, privately citing Mr. Trump’s previous statements calling the alliance “obsolete” and complaining that it had not “bothered” about terrorism. Last year, he suggested that American support for members of the alliance might be conditional on whether those members paid their financial share.

Technically, Trump is right. Only five nations actually meet the spending requirement.

Currently, only five of NATO’s 28 members—the U.S., Greece, Britain, Estonia, and Poland—meet the alliance’s target of spending at least 2 percent of their own gross domestic product on defense, a fact that is especially concerning, experts say, because of Russia’s aggressive behavior.

While the alliance increased overall defense spending in 2015 for the first time in two decades, the U.S. continues to be overwhelmingly the largest contributor, committing 3.61 percent of its GDP. The U.S. spends nearly three times as much as all European members of NATO combined.