White House press secretary Josh Earnest defended Vice President Joe Biden's criticism of Donald Trump during an overseas trip, after Trump said he would re-evaluate U.S. involvement in the North Atlantic Treaty Organization if he becomes president.

"I did not see the entirety of the vice president's remarks, but I am confident that his remarks were an effort to clear up any confusion that may exist on this front — and some of that confusion may stem from some of the rhetoric we've seen on the campaign trail," Earnest told reporters traveling with President Obama to Louisiana on Air Force One.

Earnest also reiterated that the U.S. commitment to NATO allies and to Article 5 is "ironclad."

U.S. politicians usually avoid criticizing each other while overseas, but Biden put that tradition aside Tuesday when he sought to reassure NATO allies of the United States' commitment to protect them in the face of aggression, and suggested that Trump does not understand basic tenets of the alliance.

During a stop in Riga, Latvia, Biden said that the U.S. has "never reneged on any commitment we have made" and said "our sacred honor is at stake." He then went on to argue that NATO allies shouldn't take Trump's remarks seriously about reevaluating the U.S. obligation to defend the Baltic states, "because I don't think he understands what Article 5 is."

That section of the treaty commits the U.S. and all parties to the treaty to respond to an attack on one or more of them in Europe or North America as an attack against them all, and commit to assist the country or countries attacked.

Earlier this summer, Trump raised questions about his commitment to automatically defending NATO allies against adversaries, arguing that he would first need to evaluate their contributions to the alliance.

Trump was responding to a question about whether he would defend the Baltic States if Russia attacked them. He responded that he would assist them only after reviewing whether the nations had "fulfilled their obligations to us."

"If they fulfill their obligations to us, the answer is yes," he said.