Donald Trump’s heretical positions on foreign policy are multiplying.

On his way to becoming the Republican Party’s presidential front-runner, Trump has broken with party orthodoxy on several global affairs issues, most recently casting doubt on the usefulness of NATO and suggesting that the U.S. should consider halting oil purchases from Saudi Arabia until the long-time ally helps with combat operations against the Islamic State in Iraq and Syria (ISIS).

“Definitely it’s calling into question a lot of basic assumptions that have prevailed since World War II, and it’s shocked a lot of people,” said Arthur Herman, a historian and senior fellow at the Hudson Institute.This week, the billionaire real estate mogul doubled down on statements that NATO is “obsolete.” Those remarks came in the wake of a terror attack in the treaty organization’s home city of Brussels.

Last year, Trump said that the U.S.’s alliance with Japan “doesn’t sound so fair,” since “we have to go to their defense and start World War III” if Japan is attacked, but “Japan doesn’t have to help us.”

In South Korea, where thousands of American troops have been stationed for decades, “we get practically nothing compared to the cost of this,” Trump has said.

“We have 25,000 soldiers over there protecting them. They don’t pay us. Why don’t they pay us?”

Taken together, Trump’s comments about foreign policy often hinge on the idea that the U.S. should withdraw from much of the world and negotiate a “better deal” before reengaging. In addition to casting doubts on alliances, he has also been a prominent opponent of the 12-nation Pacific Rim trade deal.

“At the basis is this sense that we’ve been suckered by the world,” said Kathleen Hicks, director of the international security program at the Center for Strategic and International Studies.

Hicks said the arrangements that Trump decries are beneficial to the United States.

“We are on the good end of the deal when it comes to why do we have alliances. Sure, we like to help other countries, but it’s for entirely selfish reasons,” she told The Hill.

“Why do we have military bases in Asia? We have used military bases in Asia because we want to be able to deal with threats far from our shores rather than close to our shores,” she added. “That’s smart and it’s actually a lot cheaper.”

Trump’s willingness to go against the grain goes beyond the troop arrangements with other nations, with his positions defying easy categorization.

Adopting a stance often associated with the far left, Trump has said that former President George W. Bush “lied” about the rationale for invading Iraq.

But taking a stance that liberals and some military professionals abhor, Trump has called for the return of harsh interrogations against terrorists, including waterboarding and “a hell of a lot worse.”

When Sen. Ted Cruz (R-Texas) appeared to equivocate about use of waterboarding earlier this year, Trump called him a “pussy.”

This month, Trump sent a shiver down the spine of military officials by suggesting that soldiers would commit war crimes, such as targeting enemies’ families, solely on his orders.

“They won’t refuse,” Trump said in a Fox News debate. “I’ve never had any problem leading people. If I say do it, they’re going to do it. That’s what leadership is all about.”

“That’s deeply disturbing, I think, in the military culture,” said Hicks, who spent more than 20 years at the Pentagon. “I think there’s a true lack of understanding of the profession of arms.

“If he ever is commander in chief, that’s going to be a huge problem.”

Foreign policy experts have struggled to define Trump’s doctrine. Many also appeared puzzled this week, when the billionaire rolled out a list of national security advisers who were unfamiliar to many.

In an interview with the New York Times, Cruz appeared to mock Trump’s “so-called foreign policy advisers.”

“They’re a pretty ragtag bunch,” said one former government official, who asked for anonymity in order to be candid. “They’ve got no experience and no strategy and no records to go on.”

Trump’s comments on foreign policy have caused increasing amounts of anxiety among conservatives, many of whom have pledged to oppose his candidacy. Some prominent Republican national security officials told The Hill this week that they might vote for Hillary Clinton over Trump in a general election matchup, if that’s what it took to keep him out of the White House.

But though the establishment is uncomfortable with Trump, a large segment of Republicans voters seem to be onboard with his “get tough” approach.

Trump benefitted the most when the political conversation turned to national security last year, following terror attacks in Paris and San Bernardino, Calif.

Even his critics acknowledge that he is tapping into an anxiety that is shared by many Americans, following long wars in Iraq and Afghanistan that cost the nation trillions of dollars and hundreds of lost lives.

The GOP front-runner also isn’t alone in questioning the U.S.’s disproportionate expenditures on global security.

In an interview published in the Atlantic this month, President Obama similarly claimed to be annoyed by “free riders” who depend on American might without making contributions of their own.

Questioning the makeup of international alliances — which in many cases date back more than a half-century and were built for a Cold War that no longer exists — is “not necessarily an unhealthy thing,” said Herman, the historian.