Obama met in the Oval Office alongside NATO Secretary General Jens Stoltenberg for more than an hour to discuss progress in the battle against ISIS and the response to last month's terror attack in Brussels, where NATO is headquartered.
While he didn't respond to questions shouted by the press about Donald Trump's derision of NATO, Obama did describe the alliance as intrinsic to American defense.
"NATO continues to be the lynchpin, the cornerstone, of our collective defense and U.S. security policy," Obama said. "It is because of the strength of NATO and the transatlantic partnership -- this transatlantic alliance -- that I'm confident that despite these choppy waters we will continue to be able to underscore and underwrite the peace and security and prosperity that has been the hallmark of the transatlantic relationship for so many decades."
U.S. officials see NATO as an essential player in the campaign against the terror group since it provides channels of command and communication between the United States and its European allies, though its traditional focus has been as a military alliance that provides for mutual defense stemming from the Cold War.
After the meeting, Obama said the leaders discussed ways to prevent ISIS from obtaining a foothold in Libya by supporting a stabilizing government there.
Obama and Stoltenberg also consulted on Ukraine, parts of which have been seized by Russian-aligned forces.
NATO has typically enjoyed broad -- if sometimes begrudging -- support from both Democrats and Republicans, who have regarded the grouping of European and North American countries as an ironclad facet of American foreign policy, though perhaps one overly reliant on American resources.
Obama has pressed European nations -- including France, Belgium and the United Kingdom -- to ramp up their military and financial support for the NATO alliance, which has long relied on significant contributions from the United States to maintain its mission of protecting member states from outside aggression.
Recent terror attacks in Paris and Brussels by ISIS-trained militants, paired with Russian activity in Eastern Europe, have led to greater commitments from some countries. The U.S. has also increased troop rotations through Eastern Europe as a display of support for NATO members in the region, nervous at signs of Russian territorial aggression.
But to GOP front-runner Trump, European NATO countries are falling far short, and he has taken to disparaging the organization on the campaign trail.
In Wisconsin this weekend, Trump argued that many of NATO's member states weren't paying their "fair share" for the protections that NATO affords.
"That means we are protecting them and they are getting all sorts of military protection and other things, and they're ripping off the United States, and they're ripping you off," Trump said at a rally in Racine. "I don't want to do that. Either they pay up, including the past deficiencies, or they have to get out. And if it breaks up NATO, it breaks up NATO."
That sentiment drew criticism from Trump's GOP rivals, who argued for a more muscular alliance to fend off threats both from ISIS and Russian President Vladimir Putin.
"NATO has to be stronger not only vis-à-vis Putin and what could happen over there in Central and Eastern Europe, but we want our allies to share intelligence with us," Ohio Gov. John Kasich said in March.
Texas Sen. Ted Cruz dismissed Trump's comments on NATO as "hopelessly naïve."
"What Donald Trump is saying is that he would unilaterally surrender to Russia and Putin, give Putin a massive foreign policy victory by breaking NATO and abandoning Europe," Cruz said.
White House Press Secretary Josh Earnest said Monday that Obama's Oval Office meeting with Stoltenberg had been "on the books long before Mr. Trump's ill-advised comments" about NATO.
Trump's argument that member nations don't pay into NATO's coffers, however, is a persistent knock on the alliance. Obama himself made direct calls for fellow leaders to increase their military spending during the last NATO summit, held in Wales in 2014.
Despite that pressure, however, only five of the 28 nations in NATO have met the benchmark of spending 2% of their gross domestic products on defense, according to NATO calculation, even as many increase their military budgets.
Obama is likely to press that issue again when he travels to Poland in July for his final NATO summit as commander in chief.
On Monday, Stoltenberg said he would continue to make that case to member nations that in times of increased security pressures, investing in military spending is essential.
"NATO is as important as ever, because NATO has been able to adapt to a more dangerous world," he said.