For months, the White House has been stuck when it comes to replacing H.R. McMaster, the president’s national security adviser.

President Donald Trump has often seemed eager to move on from the Army three-star general, who has struggled to bond with his irascible boss. And McMaster, who friends said has threatened to quit in fits of frustration and anger, has seemed eager to leave.

But efforts to move McMaster back to the Army have been stymied by two issues: Trump has had trouble finding a high-quality replacement who is willing and able to take over, and it is also not clear that McMaster, still an active-duty general officer, has any place to go in the Army.

The net result is one of the weaker National Security Councils in recent memory — a critical part of the White House that has struggled at times to corral powerful personalities in the Pentagon and State Department and advance the president’s often ill-defined foreign policy agenda.

McMaster’s has had an especially strained relationship with Defense Secretary Jim Mattis, a favorite of the president’s, who has been slow to respond to McMaster’s requests for military options to counter adversaries such as Iran and North Korea, officials said.

“He treats me like a three-star” rather than a coequal, McMaster has complained to colleagues of Mattis, a retired four-star Marine Corps general.

On Thursday, NBC News reported that the White House is preparing to replace McMaster as early as next month, the latest in a series of stories in recent weeks predicting the general’s departure.

One long-rumored candidate to become Trump’s third national security adviser is Stephen Biegun, an auto-industry executive who worked in the George W. Bush administration but is not well known in foreign policy circles, according to the officials, who spoke on the condition of anonymity to discuss internal deliberations. Biegun, who colleagues say is a steady manager and centrist, shares the president’s skepticism of big global trade deals.

White House officials insisted that no move to replace McMaster is imminent. “I was just with President Trump and H.R. McMaster in the Oval Office,” said Michael Anton, a spokesman for the NSC. “President Trump said that the NBC News story is ‘fake news’ and told McMaster that he is doing a great job.”

White House Chief of Staff John Kelly privately told colleagues on Thursday that he did not know Biegun, who was reported by NBC to have Mattis’s backing and to be a front-runner for the position.

A national security adviser’s influence is often dependent on having a close relationship with the president. But few in Washington see McMaster as speaking for Trump

In late February, McMaster said there was “incontrovertible” evidence of a Russian plot to disrupt the 2016 U.S. election. The remark drew a quick and public rebuke from the president via Twitter.

“General McMaster forgot to say that the results of the 2016 election were not impacted or changed by the Russians,” Trump wrote. “The only Collusion was between Russia and Crooked H…”

It is widely known that Trump has often grown frustrated with McMaster during meetings, complaining that he drones on too long and can be too rigid in his thinking. This summer, at a low point in their relationship, McMaster entered the Oval Office only to have Trump complain that he had already seen him that day.

McMaster reminded the president that he often needed to brief him on fast-moving events.