“We’re talking about countries that are doing very well. Then yes, I would be absolutely prepared to tell those countries, ‘Congratulations, you will be defending yourself,’” Trump said during an interview with The New York Times, adding that he would defend only countries that had “fulfilled their obligations to us” financially.
In an interview with the New York Times, Senate Majority Leader Mitch McConnell called Trump's comments a "rookie mistake."
“I am willing to kind of chalk it up to a rookie mistake,” he said. “I don’t think there is anybody he would choose to be secretary of defense or secretary of state who would have a different view from my own.”
Two additional Senate Republicans, neither of whom is attending this week’s Republican National Convention, condemned his comments, suggesting Congress would not follow his lead on the issue if he is commander-in-chief.
“As [Russian President Vladimir] 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,” Sen. Ben Sasse, R-Neb., one of the most vocal elected officials in the never-Trump movement, said in a statement.
“I can only imagine how our allies in NATO, particularly the Balkan 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,” Graham said.
“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,” Graham continued, also calling for Trump to “correct” his statements during his prime-time address Thursday evening.
Rep. Adam Kinzinger, R-Illinois, a former Air Force pilot, told ABC News he was deeply disturbed by Trump's comments about NATO.
"To protect American first you have to have strong alliances," he said. "This alliance has prevented 60 years of war."
Trump's comments, Kinzinger added, were "ridiculous and reckless," and suggest that Trump doesn't understand foreign policy.
White House spokesman Josh Earnest noted that Republicans have long accused Obama of going on a “global apology tour.”
“I guess that means that there is some irony associated with the case that’s being made by the Republican nominee at this point,” Earnest said.
The White House has declined to provide Ukraine with lethal weapons, but mainstream Republicans have long called for the president to do so.
“Just this week, we learned that the Trump campaign went to great lengths to remove a plank from the GOP platform about aid to Ukraine that would have offended Putin, bucking a strongly held position within his own party ... It is fair to assume that Vladimir Putin is rooting for a Trump presidency.”
Kingzinger, who isn't sure if he'll support Trump and has frequently criticized Trump's foreign policy pronouncements, called the platform change "curious for sure."
Secretary of State John Kerry was also pulled in to the fracas Thursday, fielding a question about Trump's comments at a press conference at the State Department.
Prefacing his comments by saying he wasn't making a statement about the presidential race, Kerry said he would restate American policy towards NATO.
"This administration, like every administration Republican and Democrat alike since 1949, remains fully committed to the NATO alliance and to our security commitments under Article 5, which is absolutely bedrock to our membership and to our partnership with NATO."
Trump was also questioned about Turkish President Recep Tayyip Erdogan's response to the failed military coup, and told the New York Times that the United States has "a lot of problems."
"Our nominee is making the same arguments you hear in Russian propaganda and that you hear from left-wing liberals," Kinzinger said of Trump's criticisms.
ABC's Ben Siegel contributed.