Donald Trump has spent much of his campaign deriding NATO allies for “ripping off” the American taxpayer and failing to contribute to the world’s most powerful military alliance. But on Wednesday, his fellow Republicans joined the chorus during a closed-door meeting with NATO Secretary General Jens Stoltenberg on Capitol Hill, according to sources inside the room.

For under an hour, senators grilled Stoltenberg, a former prime minister of Norway, about why only five members of the 28-nation club spend at least 2 percent of their gross domestic product on defense, the official amount NATO recommends each nation set aside. Some expressed particular dissatisfaction with Germany, the fourth largest economy in the world, which does not meet the 2 percent threshold.

“They’re being laggards. I can’t think of a better word for it,” Bob Corker (R-Tenn.), the chairman of the Senate Foreign Relations Committee, told Foreign Policy after exiting the meeting. “I have expressed this in Munich, I have expressed this in Davos, I have expressed this in every forum where Europeans are listening.”

For years, Corker and other U.S. officials have blasted European allies for taking for granted the disproportionate amount the U.S. contributes to the transatlantic organization. But what once was an esoteric concern confined to the halls of think tanks and embassies is now a red-hot campaign issue. Corker said Trump’s campaign rhetoric speaks to a concern he’s heard from his own Tennessee constituents, which he relayed to Stoltenberg.

“I did mention to him that there’s a populism that is taking place within our country right now, both sides of the aisle,” said Corker. “The American people know that we are a nation spending way beyond our means and when our European counterparts are not honoring their obligations as they should, at some point, there’s going to be a breaking point.”

Last year, the U.S. accounted for more than 72 percent of NATO members’ total defense expenditures, spending about $649.9 billion. The other 27 NATO members combined to spend less than 28 percent, or about $251 billion, of the total.

After exiting the meeting with Stoltenberg, Republican Sen. John Barrasso of Wyoming, added his dismay that defense spending for “very few” of America’s allies is “where it ought to be.”

“The issue of the other countries paying their full share is not an outlier view at all,” he said.

Still, a number of senators in the room emphasized that their frustrations about burden-sharing within the NATO alliance did not mean they see eye-to-eye with Trump, who has called the alliance “obsolete” and said it may have to dissolve.

“I believe NATO’s an indispensable alliance,” said Sen. Marco Rubio, who suspended his failed presidential campaign last month. “It certainly needs to be modernized but it has a real value to it.”

Democratic Sen. Chris Murphy of Connecticut said that reasonable people can disagree about the contributions of NATO members, but Trump’s open speculation that the alliance may be worth leaving is far outside the mainstream.

“I think it’s important to explain that Trump isn’t the tip of an iceberg,” Murphy told FP. “He is a tiny isolated chunk of ice out in the ocean on this.” The United States has been a member of NATO since it was formed to counter the Soviet Union in 1949.

Regardless, for longtime NATO observers, the unusually high profile of NATO scrutiny is novel for any U.S. election cycle in recent memory.

“NATO has never really gotten attention in presidential campaigns before this year’s with Trump,” said Robbie Gramer, a NATO expert at the Atlantic Council. “The fact that the only attention it has received is through this light underscores how frustrated the U.S. electorate is with its allies. And NATO really hasn’t found an effective way to combat this message.”