President Trump arrives for a news conference on the second day of the North Atlantic Treaty Organization summit in Brussels, July 12. (Brendan Smialowski / AFP/Getty Images)
Gregory Mitrovich is a research scholar at the Saltzman Institute of War and Peace Studies at Columbia University and author of "Undermining the Kremlin: America’s Strategy to Subvert the Soviet Bloc, 1947-1956."

The revelation that President Trump remains unconvinced of NATO’s value to U.S. security, arguing instead that it is an unnecessary drain on the country’s resources, has renewed doubts both in Washington and around the world regarding the survival of the alliance.

President Trump is not the first sitting president to critique NATO. Since the beginning of the alliance, many presidents have similarly expressed frustration over the costs of the United States’s European commitment. From the moment he took office in 1953, President Dwight Eisenhower, NATO’s first Supreme Allied Commander, repeatedly called for greater European defense efforts to reduce the United States’s burden.

But President Trump has taken these criticisms further. By declaring the alliance obsolete and demanding a complete U.S. withdrawal, Trump is advancing a position no U.S. president has ever taken. Eisenhower, though concerned about costs, never wavered in his commitment to NATO, even though it risked nuclear war with the Soviet Union. Why? Because Eisenhower understood the deterrent-value of NATO: Any invasion of Europe automatically meant war with the United States, thus reducing the Soviets' incentive to attack.

The general-turned-president witnessed firsthand how the United States’s unwillingness to commit to French and British security during the mid-1930s weakened their ability to deter Adolf Hitler. This was a mistake Eisenhower and his contemporaries were determined to avoid — and one that the United States must not make today.

Historians contend that French and British efforts to appease Hitler at the 1938 Munich Conference made World War II inevitable. However, appeasement was itself a byproduct of an even greater failure on the part of the World War I allies: the aborted Treaty of Guarantee. This alliance, proposed by Britain during the Paris Peace Conference in 1919, would have committed Britain and the United States to aid the French against any future German military aggression.

The United States’s commitment was necessary for the plan to work. During World War I, Germany tried in vain to keep the United States from entering the conflict, recognizing that its immense economic and financial power would lead to an allied victory. After the war, the Germans blamed their defeat on U.S. intervention. The Treaty of Guarantee would have ended any German uncertainty regarding United States’s involvement in a future war, thus placing a major brake upon German aggression.

Such a strategy of deterrence was especially important considering the Franco-German flash point left unresolved by World War I: Rhineland, Germany’s territory bordering France on the left bank of the Rhine river. German control of the region meant that they could rapidly invade France, as happened in the 1870 Franco-Prussian War, where in a matter of months France suffered a disastrous defeat. The French barely escaped a similar fate in 1914 stopping the German armies at the Marne river just outside Paris.

Marshall Ferdinand Foch, France’s military commander, insisted during the Paris Peace Conference that France be allowed to annex Rhineland and turn the Rhine river into a barrier between the two countries. The British feared annexation would only add to Franco-German animosity and proposed instead the Treaty of Guarantee, which it hoped would convince Germany’s leaders that any attack would lead to an unwinnable war.

While the British Parliament approved the treaty, the United States Senate did not. Isolationists within the Senate argued that guaranteeing a U.S. intervention violated the right of Congress to declare war under the Constitution. These critics joined with opponents of President Woodrow Wilson’s League of Nations to not only reject the Treaty of Guarantee but the entire Versailles Accord. The United States turned its back on Europe and retreated into isolationism. In 1925, French leaders arrived at a separate agreement with Germany’s new Weimar Republic for the permanent demilitarization of Rhineland in the hope that this would finally resolve the crisis.

Then came Hitler.

In 1933, Hitler became chancellor of Germany and within a year, established the Nazi dictatorship. In 1935, Hitler took the fateful step of violating the Treaty of Versailles by launching a major military buildup. Emboldened by the allies’ lack of response, Hitler took his biggest gamble, ordering the German army to enter Rhineland, a move that should have led to an immediate French response. Instead, weakened by the Great Depression and absent allied support, France sent only diplomatic protests. Convinced of the allies’ weakness, Hitler continued his expansion into Czechoslovakia and then Poland. On Sept. 3, 1939, France and Britain declared war on Germany.

Hitler was also determined to avoid the mistakes of World War I, and so he refused to make any provocations that might lead to a U.S. declaration of war. He strongly rejected his admirals’ request to launch all-out submarine warfare around the British Isles, knowing that it would lead to the sinking of U.S. merchant ships. He would wait over two years, until the Japanese attack on Pearl Harbor on Dec. 7, 1941, before declaring war on the United States.

After World War II, with the Soviet threat to Europe becoming increasingly clear, these lessons were foremost in the minds of U.S. leaders, motivating them to break with the nation’s historic isolationism and join with allies in creating NATO. And it worked. The alliance successfully stabilized Europe for 70 years, as Eisenhower and his contemporaries were confident it would.

Today’s Europe is a contradiction. While the European Union boasts a GDP and population many times that of Russia, it is consumed with political strife caused by Russian President Vladimir Putin’s strategy of chaos, including a very effective combination of hybrid-warfare, Russian social media and cyberattacks. The disastrous Brexit crisis has paralyzed the United Kingdom, and Hungary and Poland have descended into dictatorship. Russia’s hybrid warfare against Ukraine and the Baltic nations, the 2016 coup attempt against the government of Montenegro, and aggressive information warfare throughout Europe demonstrates that European stability remains in question.

The withdrawal of the United States from NATO would enable Putin to accelerate his efforts to fragment and destabilize Europe. The long-term costs for the United States are potentially immense, and any benefits are unclear at best, especially since the United States has already greatly reduced its military deployments to the continent.

The United States must continue to reassess the costs of its military commitment, while cajoling its prosperous allies into providing the majority of resources for their security. That said, the last 100 years demonstrate that European stability still requires both an unequivocal U.S. commitment and effective U.S. leadership, something President Trump is not providing. This is not the time for a U.S. withdrawal from NATO.