NATO endures on American backing while many allies demand U.S. action abroad but withhold it when asked, exposing a widening gap between rhetoric and responsibility.

NATO members are not legally required to join any member’s military operations that are not formally sanctioned by the alliance or not aimed at protecting the homelands of the membership.

But they often do just that.

Some NATO members joined the Americans in Afghanistan and Iraq on the theory that, in the post-9/11 environment, the Taliban and Saddam Hussein were dangers to all Western security.

They followed the precedent set by America’s 1999 intervention in the distant Balkans, leading a three-month NATO campaign to dismantle Slobodan Milošević’s often bloody ambitions of a Greater Serbia. The U.S. also joined the 2011 U.N.-approved, and French- and British-inspired, NATO “coalition of the willing” bombing campaign in Libya.

That effort proved a seven-month misadventure—especially since the targeted Libyan strongman Muammar Gaddafi had given up his nuclear weapons program and was desperately trying to cut a deal with the West.

When NATO members in the past have operated unilaterally to defend their own national interests, they have often called on the U.S., as NATO’s strongest member, for overt help.

For nearly 40 years, the U.S. had offered logistical, intelligence, reconnaissance, refueling, and diplomatic support to the French in their unilateral and postcolonial efforts to protect Chad from Libya and, later, Islamists.

During the 1982 Falklands War, a solitary Britain faced enormous logistical challenges in steaming halfway around the world to eject Argentina from its windswept and sparse islands.

U.S. aid was critical to the effort.

So America stepped up to help with intelligence, reconnaissance, the supply of some two million gallons of much-needed gasoline, and crucial restocking of Britain’s depleted Tomahawk missiles.

The American tilt to Britain prompted anger from most Latin American nations of the shared Western hemisphere, as well as from many Hispanic American citizens at home.

No matter—Ronald Reagan rightly saw the importance of solidarity with a NATO member and a long-time American ally. So he gave Britain a veritable blank check for American aid.

Currently, America has not asked NATO members to help bomb Iran—even though Europe, not the U.S., was in range of Iranian ballistic missiles, and soon perhaps nuclear-tipped ones as well.

Europeans are far more vulnerable to Iranian-inspired Islamic terrorism. They are more reliant on foreign oil from the Middle East, some of it passing through the Strait of Hormuz.

All the U.S. had initially asked for was basing support in disarming a common Western enemy that, for nearly half a century, has slaughtered American diplomats and soldiers and tried to kill a U.S. president and secretary of state.