Republican senators blasted Donald Trump Donald John TrumpBiden leads Trump by 36 points nationally among Latinos: poll Trump dismisses climate change role in fires, says Newsom needs to manage forest better Jimmy Kimmel hits Trump for rallies while hosting Emmy Awards MORE on Thursday for suggesting he would not defend NATO allies if they are attacked, a core purpose of the transatlantic alliance.

“Statements like these make the world more dangerous and the United States less safe," said Sen. Lindsey Graham Lindsey Olin GrahamMcConnell locks down key GOP votes in Supreme Court fight Will Republicans' rank hypocrisy hinder their rush to replace Ginsburg? Momentum growing among Republicans for Supreme Court vote before Election Day MORE (R-S.C.), himself a former Republican presidential candidate.

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“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 Putin feels: He’s a very happy man," he added.

Trump, who is set to accept the Republican presidential nomination on Thursday night in Cleveland, said in a New York Times interview published late Wednesday that as president he would not adhere to Article 5 of the NATO treaty and defend allies unless "they fulfill their obligations to us."

Trump has repeatedly called for NATO's members to all pay their share in the security alliance or spend more on their own security. Currently, five of the 28 members meet a goal to spend at least 2 percent of their gross domestic product on defense.

Trump also suggested he would not have troops based overseas, but instead deploy them during crises.

Sen. Ben Sasse (R-Neb.), a staunch critic of Trump, issued a statement touting the importance of NATO allies.

"Our friends should draw strength and our adversaries should take pause from this simple fact: Americans keep our word," he said. "As Mr. Putin revives Soviet-style aggression and the threat of violent Islam looms over European and American cities, the United States stands with our NATO allies."

Graham, a member of the Armed Services and Appropriations committees, called upon Trump to "correct" his statements on Thursday night when the Republican National Convention addresses national security.

"If Mr. Trump is serious about wanting to be Commander in Chief he needs to better understand the job which is to provide leadership for the United States and the free world," he said.

“Mr. Trump has shown the ability to correct statements such as this. I hope he will do so tonight when the world is watching.”

NATO officials avoid commenting on the internal affairs of member nations, but its head Jens Stoltenberg took the rare step of responding to Trump's comments in a statement.

"Solidarity among Allies is a key value for NATO," he said. "We must defend one another. We have seen this in Afghanistan, where tens of thousands of European, Canadian, and partner nation troops have stood shoulder-to-shoulder with US soldiers."