Since its creation in 1949 , NATO has been history’s most successful and longest lasting military alliance. Now, that is changing — and for the wrong reasons. For the only time in its 77 years, NATO is threatened not only by an external adversary but, frighteningly, from within. And this new threat is very real.

President Donald Trump’s administration has made several unambiguously clear demands on NATO. First, European members must assume greater, if not virtually all, responsibility for the defense of Europe. This will allow the U.S. to focus on its main priorities of homeland defense and averting a Chinese invasion or assault on Taiwan. The Pentagon is also finalizing plans for redeployment of U.S. troops from Europe to reinforce the other two actions.

It is possible that for the first time the next Supreme Allied Commander Europe will be a European, not an American .…