In our personal lives, we know that many important ties are not necessarily permanent. Friendships end; marriages break up; once-loyal consumers stop shopping at one store in favor of a different one. If a relationship no longer serves the needs of one or more parties, it usually makes sense to move on.
That logic holds for partnerships among nations. The 19th-century British prime minister Lord Palmerston said, "Nations have no permanent friends or allies; they only have permanent interests." But the United States government has often behaved as though our membership in NATO should be eternal.
There is no reason it should be. Well, maybe one reason: that Donald Trump has the urge to get out. Because his motives are rooted in ignorance, petulance and a desire to appease Vladimir Putin, it's easy to miss that there is a legitimate case for a gradual and orderly American withdrawal from the alliance.
Formed in the aftermath of two world wars that began in Europe, NATO was created for two basic purposes: deterring communist aggression and preserving peace. It performed that function well, despite many disagreements among the members, which now number 29 in Europe and North America. The postwar military alliance enabled Western Europe to build freedom and prosperity, in vivid contrast with the brute misery on the other side of the Iron Curtain.
But the original purposes have gone the way of the Habsburg empire. The regime left by Lenin and Stalin collapsed. Eastern European nations gained their independence from Moscow. Germany grew into a model democracy that bothers no one.
Today, Russia has a dictatorial president who jails and kills dissidents, occupies a chunk of Ukraine, and plots to undermine Western systems — most notably ours. But the military threat that the Kremlin once represented has shriveled.
Putin's chief focus is preserving his own power. Whatever military power he can command pales next to the combined might of the European nations in NATO — which together spend four times more on defense than Russia does. Britain and France also have their own nuclear weapons.
Harvard international relations scholar Stephen Walt notes that the European Union has three times the population of Russia and eight times the gross domestic product. "Russia's long-term prospects are gloomy as its population shrinks and ages and as oil and gas become less and less important in the global economy," he wrote in Foreign Policy. "Russia can cause trouble of various kinds in nearby areas, but there is no chance that it could expand significantly (or effectively rule any territories it seized)."
NATO also served to keep Germany, the source of so much trouble in the first half of the 20th century, from going rogue once again. But Germans have become addicted to multilateralism. Over the past couple of decades, Berlin has more often felt the need to restrain Washington than the other way around.
The end of the Cold War left NATO searching for a reason to exist. It expanded to include countries on Russia's doorstep, without any sound strategic rationale. The enlargement fostered anxiety and resentment in the Kremlin while committing the U.S. to defend countries that most Americans would not want their sons and daughters to die for.
Trump has often griped that our allies expect us to carry too much of the load. That complaint has a distinguished pedigree. In 2011, Robert Gates, who was defense secretary under George W. Bush and Barack Obama, castigated allies "who enjoy the benefits of NATO membership but don't want to share the risks and the costs."
Eight years later, not much has changed. The U.S. spends 3.6 percent of its GDP on defense. According to NATO, just five European countries spend as much as 2 percent, and Germany spends just 1.2 percent. If our allies were obliged to provide for their own defense without us, they could easily afford to do so.
But a long-standing and valuable relationship should be ended only for defensible motives, under a rational plan and at an opportune time. If Trump abandons NATO, though, these conditions are not likely to be met.
Under a serious president with a serious approach to foreign relations, it would be possible to have a serious debate about how to phase out America's military role in Europe in a prudent, responsible way. Under Trump, even good ideas can become bad policies.
Steve Chapman blogs at http://www.chicagotribune.com/news/opinion/chapman. Follow him on Twitter @SteveChapman13 or at https://www.facebook.com/stevechapman13. To find out more about Steve Chapman and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.