The North Atlantic Treaty Organization boasted on Twitter that the four World Cup semifinalists — France, the U.K., Belgium and Croatia — are members of the alliance. The U.S. failed to qualify for the tournament, so on the soccer field at least, the alliance can hold its own. But could the common defense pact survive without its dominant military power?

Some military experts have asked that question since U.S. President Donald Trump's election. Although he has repeatedly criticized European allies for not spending enough on defense (at least from the U.S. perspective), Trump is very unlikely to announce a pullout at the organization's summit on July 11-12. Extricating the U.S. would take more time than Trump has in the White House, and it would probably be blocked by Congress. Moreover, Europeans don't want the U.S. out.

But maybe they should call his bluff, if only to drive home that the protection the U.S. is supposedly providing isn't as vital as Trump appears to believe.