National security adviser John Bolton is reportedly attempting to undermine Defense Secretary Jim Mattis by spreading rumors that he is on his way out of the Trump administration.

In what is the latest episode of reported drama in Trump's inner orbit, the a source told Foreign Policy that Bolton and his deputy Mira Ricardel have the "knives out" for Mattis, with whom they have a dissenting outlook on matters like the Iran deal, North Korea, and Pentagon appointees.

National Security Council spokesman Garrett Marquis dismissed the allegations of an alleged whisper campaign. “Ambassador Bolton is working closely with Secretary Mattis to implement the president’s agenda,” the spokesman told the outlet. “Any indication otherwise is flatly wrong.”

The report comes only days after the latest round of rampant speculation about Mattis, after Trump appeared to suggest in a "60 Minutes" interview that he may depart in the near future. "Gen. Mattis is a good guy. We get along very well. He may leave. I mean, at some point, everybody leaves. Everybody. People leave. That's Washington," Trump said, after noting that he thinks Mattis is "sort of a Democrat."

Mattis has only shrugged off any talk about his future. A Defense Department spokesman said after that interview, "Secretary Mattis is laser-focused on doing his job."

And yet, the report also follows indications that Mattis is increasingly being sidelined. Over the weekend, Trump abruptly announced he’s ready to scrap the 1987 Intermediate-Range Nuclear Forces Treaty with Russia, which has banned the development and deployment of land-based intermediate-range missiles. Bolton favored such a move, while Mattis, after recently briefing NATO defense ministers in Brussels, seemed to indicate he preferred to pressure Russia to comply with the treaty rather than scrap it.

A Trump administration official who spoke with Foreign Policy stressed that Mattis is “highly regarded” within the Cabinet and in Congress. The official added that, “Mira and Bolton are the only ones who benefit if Secretary Mattis leaves."

While the report suggests another point of contention is the National Security Council neglecting to hold regular briefings including the Pentagon, though White House officials said a national policy breakfast discussion takes place "almost weekly."

The reported tension between Bolton and Mattis in the Trump administration have stretched back to when Bolton first came aboard in the spring.

Mattis told reporters in March that he had "no reservations, no concerns at all about working with" Bolton shortly before Bolton started as national security adviser, and suggested that differing opinions would be a good thing.

“I hope that there are some different worldviews. That’s the normal thing you want, unless you want groupthink,” Mattis said. “We’re going to sit down together. I look forward to working with him. Last time I checked, he's an American. I can work with an American, OK?"

Later that month, When Bolton met Mattis at the Pentagon, Mattis cracked a joke about meeting the devil.

“It’s good to finally meet you,” Mattis told the former ambassador to the United Nations. “I heard that you’re actually the devil incarnate and I wanted to meet you.”

[Also read: Jim Mattis to dispatch 800 troops to US-Mexico border ahead of caravan]