When NATO Secretary General Jens Stoltenberg emerged from his meeting with President Obama, it didn't take long for reporters to ask a question about Donald Trump.
The GOP presidential front-runner has questioned why NATO even still exists. Trump has dismissed the 28-nation alliance as "obsolete," and designed to fight an enemy that doesn't exist anymore, the Soviet Union.
Some of President Obama's comments about NATO also could perhaps be viewed as a not so subtle swipe at Trump.
"The NATO alliance is the lynchpin, the cornerstone of our collective defense," the president said in his Oval Office remarks.
Continuing what have become almost daily broadsides, the president recently said Trump doesn't know much about foreign policy, or "the world generally." That came after Trump had said Japan and South Korea should perhaps have nuclear weapons to defend themselves.
Obama said the session reinforced "the importance of us staying focused on ISIL and countering the terrorism that has seeped up into Europe and around the world."
While NATO isn't a member of the U.S.-led coalition fighting ISIS, most of its individual members like Great Britain, France and Turkey, to name a few, are.
The president also highlighted a number of other global challenges where NATO continues to play a role.
For example, working with members Greece and Turkey to deal with the humanitarian crisis caused by the exodus of Syrian refugees. NATO also continues to back Ukraine where Russia has captured territory in Crimea.
Meanwhile, for all the criticism Trump has taken for his recent foreign policy pronouncements, he did raise an issue about NATO that echoes an Obama administration concern.
At a recent rally in Wisconsin, using a familiar phrase, Trump accused those NATO members of, "ripping off the US." Trump went on to say that if those members didn't pay up, he would be okay with NATO breaking up.
On Monday, Obama's spokesman struck a more diplomatic tone when asked if the President was satisfied with spending levels now.
"There are some NATO countries that meet that and some that don't," Josh Earnest said.
Bottom line: While President Obama strives to make it clear that America's relationship with NATO is essential, Trump continues to insist it's not.
This article originally appeared on NBCNews.com.