The Pentagon is exploring options that would give President Donald Trump the ability to move National Security Adviser H.R. McMaster out of his role in the White House and back to the military, according to a new report from CNN.

According to six defense and Trump administration officials who spoke with CNN, the Pentagon is quietly searching for a four-star military position in the Army or the Defense Department that would function as a promotion for McMaster after months of mounting tension between the President and his national security adviser.

Trump has reportedly been privately irritated with McMaster for months, mostly stemming from issues Trump has with McMaster’s personality and style, according to a senior Republican source who spoke with CNN. Trump believes McMaster is condescending and unfriendly, the source told CNN.

The President’s frustration with McMaster became public over the weekend when Trump criticized him on Twitter. Trump was likely responding to McMaster’s remarks about the “incontrovertible” proof that Russia meddled in the 2016 election.

“General McMaster forgot to say that the results of the 2016 election were not impacted or changed by the Russians and that the only Collusion was between Russia and Crooked H, the DNC and the Dems,” Trump said on Twitter. “Remember the Dirty Dossier, Uranium, Speeches, Emails and the Podesta Company!”

According to several sources who spoke with CNN, the White House considered replacing McMaster last fall, but decided against it to avoid the criticism of having to appoint a third national security adviser in less than a year. McMaster replaced Michael Flynn after he resigned over the controversy surrounding his contacts with Russian officials and has since pleaded guilty to lying to the FBI about those contacts.