Things aren’t so peachy anymore between President Donald Trump and Defense Secretary Jim Mattis, according to recent reports.

Helene Cooper at the New York Times and David Cloud at the Los Angeles Times have both published accounts of the increasingly frayed relationship between the president and the retired Marine general, whom Trump previously revered. The pair have gone from sharing burgers over briefings to distant communications and diverging opinions on matters of national security.

Trump has reportedly stopped calling Mattis “Mad Dog” — a nickname Mattis didn’t like in the first place — and has instead, according to Politico, begun calling him “Moderate Dog” behind closed doors.

The very thing that endeared Mattis to allies, Democrats, and members of the national security establishment — a sense that he checked some of Trump’s more disruptive foreign policy impulses — has become the thing chafing his relationship with the president.

The New York Times reports that Trump has started to worry that Mattis is a Democrat at heart, and White House officials have expressed annoyance at what they see as the defense secretary’s less-than-eager response to the president’s requests. Mattis initially slow-walked Trump’s decision to ban transgender troops from serving in the military and shot down a White House proposal to stop family members from accompanying troops to South Korea.

According to the LA Times, most of the Pentagon was “blindsided” when Trump said he would suspend military exercises with South Korea as a gesture of goodwill to North Korea after meeting with its leader Kim Jong Un in Singapore in June. Trump and Mattis also reportedly have different takes on the White House’s proposed “space force.” Mattis publicly questioned the need for it; later, after the White House had announced the Pentagon would create the new branch, he said he was just against “rushing” to do so. The pair have also disagreed over NATO policy and Trump’s decision to withdraw the United States from the Iran nuclear deal.

There has been little public indication that things aren’t well between Trump and Mattis. The retired general is averse to media attention and hesitant to criticize the president publicly, and so he’s stayed largely silent.

One exception came earlier this month when Bob Woodward’s book, Fear: Trump in the White House, quoted Mattis telling associates that Trump had the understanding of “a fifth- or sixth-grader” after a National Security Council meeting in which President Trump questioned the United States’ military presence on the Korean Peninsula.

Mattis has denied Woodward’s reporting. “The contemptuous words about the President attributed to me in Woodward’s book were never uttered by me or in my presence,” he said in a relatively rare public statement. “While I generally enjoy reading fiction, this is a uniquely Washington brand of literature, and his anonymous sources do not lend credibility.”

The White House also insists all is well with the Pentagon. When Washington Post columnist Josh Rogin reported at the start of September that Trump was considering potential replacements for Mattis, Trump denied it. The president said he is “very happy” with Mattis and the “victories” he’s delivering. He also said Mattis’s statement denying the remarks Woodward reported was “the nicest quote about me I think I’ve ever had.”

Thank you General Mattis, book is boring & untrue! https://t.co/Bq79ZjF3Dk — Donald J. Trump (@realDonaldTrump) September 5, 2018

Trump used to love Mattis

Mattis was for quite some time seen as one of the few figures surrounding Trump who could survive the president’s often volatile temperament. He outlasted former Secretary of State Rex Tillerson and National Security Adviser H.R. McMaster, and even though he hasn’t been the best of fits with their replacements, Mike Pompeo and John Bolton, he’s stayed on.

As Vox’s Alex Ward explained earlier this year, Mattis, at least initially, appeared to have “broken the code” of working in the Trump administration by staying out of the press and doing his best not to make news.

“I think the way he’s dealing with the press both reflects his own natural instincts about not wanting to be in the limelight,” Doug Wilson, a Pentagon senior spokesperson in the Obama administration, told Ward at the time. “And it also reflects the realities of this administration where focusing on your job and putting your nose to the grindstone is the best way to ensure you get to keep doing your job.”

But if recent reporting is any indication, that’s no longer enough to keep Mattis on the good side of a president whose foreign policy beliefs align more with newer members of his staff, such as Bolton.

Still, the Pentagon continues to insist all is well — and that Mattis is focused on the task at hand.

Dana White, the Pentagon’s press secretary, told the New York Times there’s “no daylight” between Mattis and Trump “when it comes to the unwavering support of our military,” adding that it’s “up to the president” to decide what he wants to do. White told the LA Times that Mattis is “laser-focused on doing his job — ensuring the US military remains the most lethal force on the planet.”