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(CNN) —  

President Donald Trump is ready to oust Lt. Gen. H.R. McMaster and find a new national security adviser before the North Korea meetings in May, multiple sources told CNN Thursday.

The move may be delayed because there’s no final decision on a replacement, sources say. The timing of an announcement is unclear – one source said it could come as soon as Friday, though others say that is unlikely.

White House press secretary Sarah Sanders pushed back on reports that McMaster may be headed out the door in a tweet, saying,”Just spoke to @POTUS and Gen. H.R. McMaster - contrary to reports they have a good working relationship and there are no changes at the NSC.”

Any delay in the move is also because McMaster is trying to nail down his next steps, one of the sources said.

The shake-ups come as Trump signaled this week that he’s prepared to dismiss aides with whom he’s clashed as he works to surround himself with advisers more aligned with his populist agenda and freewheeling style.

On Tuesday, the President fired Secretary of State Rex Tillerson and told reporters at the White House he was near having his ideal team.

“I’m really at a point where we’re getting very close to having the Cabinet and other things that I want,” Trump told reporters on the South Lawn on Tuesday, moments after announcing Tillerson’s firing.

Amid speculation about McMaster’s fate, CNN has reported that the three-star general has been in discussions with the Hoover Institution.

As recently as March 8, the White House was denying reports that McMaster was on his way out, with Sanders declaring on “Fox & Friends” that “General McMaster’s not going anywhere.”

Several sources told CNN that the push for a replacement comes after months of personal tension between McMaster and Trump.

Trump has privately expressed irritation with McMaster stemming from differences in “personality and style,” a senior Republican source said.

The two have never gotten along, and Trump continues to chafe at McMaster’s demeanor when he briefs him, feeling that he is gruff and condescending, according to a source who is familiar with his thinking.

Sources with knowledge of McMaster’s standing in the White House have repeatedly said that he has been on thin ice for months.

There was discussion in the West Wing about replacing him last fall, but he ultimately survived because officials, including the President himself, were skeptical about the optics of appointing a third national security adviser in less than a year, several sources told CNN. Trump’s first national security adviser, Michael Flynn, resigned within a month of taking the job amid controversy over his contact with Russian officials.

McMaster was also retained at the time due to the White House’s challenge attracting top talent for jobs in the administration due to Trump’s “blacklist” of individuals who have criticized the President, his personality and the Russia investigation, according to a senior Republican source.

CNN’s Dana Bash, Nicole Gaouette, Jim Acosta and Jeff Zeleny contributed to this report.