“If the Russians sense a window of opportunity, they will use it to their advantage,” warns Lt. Gen. Riho Terras, who commands Estonia’s military. “We must make sure there’s no room for miscalculation.” Regrettably, many of NATO’s political leaders -- and the populations that keep them in office -- are widening the window of miscalculation and sending Moscow the very worst signal at the very worst time.

According to a recent Pew survey, there’s no majority support in Britain, Spain, Italy, Germany, France or Poland for defending a fellow NATO ally from Russian attack. As if to answer their wayward publics, NATO officials turned to Twitter to declare: “NATO commitment to Article 5 is rock solid… #AlliedStrong.”

Article 5 of the North Atlantic Treaty is NATO’s all-for-one collective defense clause, declaring that “an armed attack” against any member of the alliance “in Europe or North America shall be considered an attack against them all” and obliging members to come to the defense of the attacked ally. In short, Article 5 is the heart and soul of the alliance, which means this problem of political will within NATO cannot be solved with hashtags and tweets.

Some of us have been concerned about the health of Article 5 ever since NATO’s halfhearted intervention in Afghanistan. It pays to recall that Afghanistan was an Article 5 operation -- the outgrowth of the first and only time the alliance has invoked its all-for-one defense clause, which was on September 12, 2001. Yet in the years that followed, it became clear that some allies don’t take Article 5 as seriously as others. If they did, European defense spending wouldn’t have shrunk by 15 percent after 9/11; Washington wouldn’t have been reduced to begging for more troops in Afghanistan; and the troops that were sent wouldn’t have had limits on how, where and when they engaged the enemy: Italy didn’t permit its fighter-bombers in Afghanistan to carry bombs. German troops were required to shout warnings to enemy forces -- in three languages -- before opening fire. Some allies repeatedly failed to deliver on troop pledges. As a consequence, the United States contributed 71 percent of all forces, and non-NATO members Australia, Georgia, and Sweden deployed more troops than many founding members of the alliance.

Then, with the U.S. “leading from behind” in Libya, NATO’s European contingent was found woefully lacking in precision-guided munitions, targeting and jamming capabilities, mid-air refueling planes, reconnaissance platforms, drones, and command-and-control assets -- just about everything needed to conduct a 21st-century air war. This is what happens when nations, in effect, stop investing in the common defense. As the British government concludes, years of underfunding have led to “alarming deficiencies in the state of NATO preparedness.”

To address those deficiencies, NATO headquarters has been nagging members to invest two percent of GDP in defense for years. Yet only a handful of members meet that standard, and a look behind the numbers suggests that even this comes with an asterisk. In addition to the U.S. (which invests 3.6 percent of GDP on defense -- and falling fast), Greece (2.4 percent), Poland (2.2 percent), Britain (2.1 percent) and Estonia (2 percent) will technically hit the 2-percent target this year. But Greece is a political-economic basket case and has been cozying up to Moscow. Poland only recently put itself on the path to 2 percent. Even after using accounting tricks to shift monies previously under the purview of the Foreign Office to the military, Britain will struggle to remain above the 2-percent threshold. And tiny Estonia fields just 6,000 troops.

Further down the list, some of NATO’s largest and richest members -- nations that, unlike Estonia, have the resources to contribute to the common defense -- are either investing their dwindling defense resources somewhere other than NATO’s eastern flank or getting out of the national-defense business altogether: France (1.8 percent) is reversing some defense cuts -- but largely to counter jihadists inside France. Turkey (1.7 percent) is drifting away from NATO, Europe, and the West. Germany (1.2 percent) seems to refuse most meaningful requests made by NATO, and its army used painted broomsticks to simulate machine guns during a 2014 NATO exercise. Italy (1 percent) has slashed defense spending 12 percent since last year. Canada (1 percent) has seen a decline in defense spending since 2012, even as its economy booms.

All of this strikes at the very heart of NATO’s credibility, capability, and cohesiveness. After all, an ally that promises to help only where the scenery is serene, only if there’s no financial cost, only with broomsticks, is not much of an ally. Yet that’s an accurate description of how too many NATO members view their post-Cold War role -- and, apparently, how populations in several NATO nations view defending Eastern Europe.

Doubtless, Vladimir Putin has been a keen observer of all of this.

“In more peaceful times, it was right to reduce defense spending,” NATO Secretary General Jens Stoltenberg soberly observes. “But we do not live in peaceful times.” Key NATO members seem oblivious to this reality -- even as Russia’s resurgent military menaces the Baltics, buzzes NATO airspace, and invades sovereign neighbors.

If this litany isn’t enough to shake NATO’s inward-looking publics out of their post-Cold War lethargy, what is?

Interestingly, there is something NATO’s rich, developed European members are ready and willing to defend against: African immigrants. The EU has authorized, and several of its members have launched, a naval operation in the Mediterranean to “identify, capture and destroy vessels” carrying migrants from Africa. In other words, Western Europe can find the resources and summon the will to act when it wants to do so.

NATO’s lukewarm members counter that they have scaled up the number and size of military exercises, launched a reassurance initiative for Eastern Europe and beefed up the NATO Response Force (NRF).

However, the very fact that NATO had to scramble to take these steps after Russia invaded Ukraine and annexed Crimea underscores that the alliance had not conducted the quality and quantity of exercises needed to illustrate its seriousness, had not assured Eastern Europe or Moscow of its deterrent capabilities, had not invested enough in the much-ballyhooed NRF, and had not learned anything from Russia’s 2008 invasion of Georgia. Moreover, these reactions have a short-term feel; defense spending and ingrained public attitudes, on the other hand, reflect longer-term realities.

Now, more than any time since the fall of the Berlin Wall, NATO must devote adequate resources to deterrence -- and redouble efforts to educate its publics on the enduring mission of the alliance.

That mission is to keep the peace by deterring Moscow. That’s what Article 5 is all about. That’s why NATO was formed in 1949, why it survived after 1989, and why East European nations so desperately wanted to join in the years after -- as a hedge against the very scenario now unfolding. But if NATO’s members don’t take Article 5 seriously, neither will NATO’s enemies.

Alan W. Dowd is a senior fellow with the Sagamore Institute Center for America’s Purpose.