U.S. Secretary of State John Kerry has assured NATO allies in Eastern Europe that the United States remains "fully committed" to defending them.
"I want our NATO partners to be clear where we stand. This administration, like every single administration Republican or Democratic alike since 1949, remains fully committed to the NATO alliance and to our security commitments" under Article 5 of the North Atlantic Treaty, which states that an attack on any member state is considered an attack on every NATO member, he said in Washington on July 21.
Kerry added that this commitment is "absolutely bedrock to our membership" in NATO.
The top U.S. diplomat was responding to remarks by U.S. Republican presidential candidate Donald Trump in an interview with The New York Times on July 20, saying if he were president he would not automatically come to the aid of the Baltic states if they were invaded by Russia.
Trump said he would first review whether such countries had "fulfilled their obligations to us" before deciding whether to come to their aid in the event of an attack by Russia.
The comments follow previous statements by Trump questioning the commitment of unnamed NATO members who he has said are not contributing as much as they should to the alliance, complaining that Washington was shouldering too much of NATO's financial burden.
Trump said U.S. allies would "adjust to his approach" and he would "prefer to be able to continue" existing agreements. But he said that would only be possible if U.S. allies stop taking advantage of Washington's generosity to always foot the bill, which he said the country can no longer afford.
Trump's comments provoked sharp responses throughout the day on July 21, with NATO Secretary-General Jens Stoltenberg saying, "Two world wars have shown that peace in Europe is also important for the security of the United States... We defend each other."
British Defense Secretary Michael Fallon said NATO's mutual defense guarantee is a commitment that comes without any "conditions or caveats."
Estonian President Toomas Hendrik Ilves tweeted that his country was one of the few to meet the minimum defense expenditure requirement Trump touted and noted pointedly that Estonia "fought, with no caveats" on behalf of the United States in Afghanistan.
The only time the treaty's mutual-defense clause has been invoked was in 2002, when NATO deployed one-third of the troops sent to Afghanistan for a decade. More than 1,000 non-American troops have died in Afghanistan.
Even Trump's allies in the Republican party balked at his stance.
Senate Republican leader Mitch McConnell said he totally disagreed with Trump's statement but would "chalk it up to a rookie mistake."
McConnell called NATO "the most successful military alliance in the history of the world," in a Facebook interview with The New York Times.
"My hope is that if Donald is elected president, we can convince him to change his mind on it," said Senator Marco Rubio, a former rival of Trump in the Republican primary elections who now supports him.
"Statements like these make the world more dangerous and the United States less safe," said Republican Senator Lindsey Graham, a bitter foe of Trump. "I can only imagine how our allies in NATO, particularly the Baltic states, must feel after reading these comments from Mr. Trump. I'm 100 percent certain how Russian President [Vladimir] Putin feels: He's a very happy man,"
With reporting by AFP, Reuters, AP, and The New York Times