President Trump's frustrations with national security adviser John Bolton are boiling over and he is considering removing his hawkish foreign policy aide, according to sources close to the White House.

Several insiders said candidates to replace Bolton have already emerged, including retired Army Col. Douglas Macgregor and Ricky Waddell, assistant to the chairman of the Joint Chiefs of Staff. Macgregor recently spoke with Trump, but it’s unclear what they discussed, according to a source.

“It’s certainly become clear to anyone who knows the way this president operates that Bolton’s time is coming to an end. It’s just unclear if he has a few more weeks or a few more months,” one former White House official told the Washington Examiner.

A second former White House official said they heard Trump is "fed up with Bolton.” A third said, "the president has seriously been considering other options.”

A different former senior administration official said, “I’d be surprised if [Trump] doesn’t want Bolton to quit. That's kind of his MO.”

Bolton’s aggressive approach to U.S. enemies has at times disconcerted the president, who regularly jokes that Bolton is hoping to enjoy a war somewhere. He frustrated Trump quarterbacking a failed uprising in Venezuela. Last week, Trump publicly disagreed with Bolton's long-sought goal of "regime change" in Iran and blessed dovish Sen. Rand Paul's request to act as an emissary.

Macgregor, an occasional Fox News guest, holds views close to Trump’s own. He has questioned the value of intervening in Afghanistan, Iraq, and Syria. He was a commander in the Gulf War tank battle for which former national security adviser H.R. McMaster won a Silver Star.

Waddell, a former deputy national security adviser under McMaster, would be a more conventional pick. He’s seen as a favorite of Secretary of State Mike Pompeo, with whom Bolton has vied for leadership on foreign affairs.

Neither Waddell nor Macgregor would comment.

One problem for Bolton is in-house tension with acting White House chief of staff Mick Mulvaney. The Washington Post reported this month that Bolton and Mulvaney are “barely on speaking terms” and that Mulvaney installed a deputy, Rob Blair, who "regularly battles" Bolton allies.

A source who knows Mulvaney told the Washington Examiner on Thursday that "Mulvaney as of last week was interested in removing John Bolton from his job. That's true. That is not speculation."

Mulvaney was confronted in his office after the Washington Examiner asked Bolton’s office to comment. “I have never spoken to anybody about John Bolton’s job,” Mulvaney said on the spot.

Emma Doyle, Mulvaney’s principal deputy chief of staff, confirmed the quote and said Mulvaney stood by it.

Some insiders think Bolton is safe, at least for now.

One well-connected former White House official said they "would be surprised" if Trump was actively interviewing candidates.

Another person close to the White House, meanwhile, said they heard Trump is starting to talk to people about the job, but later came to believe Bolton is “not going anywhere” before the 2020 election.

“Reporting on unverified meetings, denials from the White House, and no sourcing from senior officials in the administrations is, sadly, fake news,” a White House official said.