NATO Takes Issue With Donald Trump’s Comment on Defending Allies

In an unusual response to a political debate, alliance’s head says members ‘defend one another’

WASHINGTON—The head of the North Atlantic Treaty Organization took the unusual step of wading into the U.S. presidential campaign on Thursday after Republican nominee Donald Trump rekindled a foreign policy debate by saying the U.S. may not come to the aid of alliance members if they are attacked by Russia.

“I will not interfere in the U.S. election campaign, but what I can do is say what matters for NATO,” NATO Secretary General Jens Stoltenberg said. “Solidarity among allies is a key value for NATO.”

Without mentioning Mr. Trump by name, Mr. Stoltenberg said alliance members “defend one another.” Article 5 of the 1949 treaty that established NATO stipulates that an attack on one member represents an attack on all and requires the alliance to come to the defense of any country attacked.

In an interview with the New York Times , Mr. Trump questioned the collective defense provisions of the NATO treaty on monetary grounds, saying that many members weren’t paying their fair share. He told the paper that if Russia attacked the Baltic States, which are NATO members, he would decide whether to defend them only after reviewing “if they have fulfilled their obligations to us.”

Such a change in policy would put the alliance into question and fundamentally rewrite the rules of European security that have been in place since the end of World War II.

The White House said that President Barack Obama has an “ironclad” commitment to NATO allies. “There should be no mistake or miscalculation made about this country’s commitment to our Transatlantic alliance,” said White House press secretary Josh Earnest.

Mr. Trump’s comments prompted an outcry from politicians and policy experts on both sides of the aisle, who warned that the U.S. couldn’t go back on its word.

“Statements like these make the world more dangerous and the U.S. less safe,” U.S. Senator Lindsey Graham (R., S.C.) said in a statement, adding they would make Russian President Vladimir Putin “a very happy man.”

“The Republican nominee for president is essentially telling the Russians and other bad actors that the U.S. is not fully committed to supporting the NATO alliance,” Mr. Graham said, adding he hoped Mr. Trump would correct himself.

Sen. Ben Sasse (R., Neb.), a critic of Mr. Trump, said the U.S. stands with its allies in NATO. “Our friends should draw strength and our adversaries should take pause from this simple fact: Americans keep our word,” Mr. Sasse said.

At the Republican National Convention in Cleveland, some lawmakers who said they plan to vote for Mr. Trump criticized his comments on NATO, including Rep. Bill Huizenga (R., Mich.).

“I wholeheartedly reject that,” he said. “We have a treaty, we have an obligation. We’re the U.S. —we can’t diminish ourselves by saying we are not going to live up to long-held, commonly accepted treaties like that.”

Kurt Volker, a former U.S. Permanent Representative to NATO under President George W. Bush and Mr. Obama, said Mr. Trump’s comments are worrying allies in the alliance.

“They are really nervous,” Mr. Volker said. “They don’t know what it means. They have a hard time believing the U.S. would do such an about-face on policy, and frankly nobody really knows what U.S. policy would really be.”

Mr. Trump’s campaign didn’t immediately respond to a request for comment.

Mr. Trump has echoed the Obama administration’s complaints that members of NATO don't pay their fair share in the alliance, which has asked all members to spend 2% of their gross domestic product on defense.

But while the Obama administration has urged European member states to pay more, it hasn’t tied U.S. commitments under the treaty to the payment issue.

State Department Spokesman John Kirby declined to comment specifically on Mr. Trump’s remarks but said the Obama administration’s policy mirrors that of administrations dating back to 1949, which is “to hold firm to our commitment to the NATO alliance.”

Responding to criticism that Europe doesn't spend enough on defense, Mr. Stoltenberg said that this year spending had increased by European allies and Canada by $8 billion.

Former Speaker of the House Newt Gingrich, who has endorsed Mr. Trump, came to the nominee’s defense in an appearance on “CBS This Morning,” during which he said NATO countries should indeed worry about the U.S. commitment.

“They ought to worry about commitment under any circumstances,” Mr. Gingrich said. “Every president has been saying that the NATO countries do not pay their fair share.”

Mr. Gingrich questioned whether it was worthwhile for the U.S. to defend countries close to Russia such as Estonia that are members of NATO.

“Estonia is in the suburbs of St. Petersburg,” he said. “I’m not sure I would risk a nuclear war over some place which is in the suburbs of St. Petersburg. I think we have to think about what does this stuff mean.”

Estonian President Toomas Hendrik Ilves took to Twitter in response, saying Estonia is one of five NATO allies in Europe that have in fact met the 2% commitment. He also pointed out that Estonia fought in Afghanistan after the NATO alliance triggered Article 5 for the only time in its history—in defense of the U.S. after the Sept. 11, 2001, attacks.

“We are equally committed to all our NATO allies, regardless of who they may be,” Mr. Ilves said on Twitter. “That is what makes them allies.”

Former Secretary of State Hillary Clinton’s presidential campaign quickly seized upon Mr. Trump’s comments.

“Ronald Reagan would be ashamed. Harry Truman would be ashamed,” said Jake Sullivan, senior policy adviser to Mrs. Clinton’s campaign, in a statement. “Republicans, Democrats and Independents who (helped) build NATO into the most successful military alliance in history would all come to the same conclusion: Donald Trump is temperamentally unfit and fundamentally ill-prepared to be our commander-in-chief.”

Mr. Sullivan said the Republican nominee’s comments “flatly contradicted” a Wednesday convention speech by Republican vice presidential candidate Mike Pence, who said Mr. Trump would stand with the U.S.’s allies.

Over the course of the campaign, Mr. Trump has taken other unorthodox positions that have roiled the national security establishment.

This year, the Republican nominee said it wouldn’t be so bad if Japan, South Korea and Saudi Arabia obtained nuclear weapons of their own, saying that nuclear proliferation would “happen anyway.”

In the New York Times interview on Wednesday, he said the U.S. wouldn't pressure Turkey or other countries to stop authoritarian behavior, saying Washington doesn’t have a right to lecture others and should fix its own mess first.

—Julian E. Barnes in Brussels, Damian Paletta in Washington and Kristina Peterson in Cleveland contributed to this article.