The relationship between President Donald Trump and Defense Secretary James Mattis has deteriorated to the point where Trump is worried that Mattis is secretly a Democrat, according to a Saturday New York Times story.

While Trump still publicly stands by his defense secretary, the Times paints a picture of a president who is increasingly resentful of Mattis’ apolitical stance and the perception that Mattis is the only adult in the room.

For his part, Mattis is reportedly getting tired of having to be that adult. He clashed with Trump over NATO and war games with South Korea, and the hiring of national security advisor deputy Mira Ricardel has further strained his relationship with the White House.

Mattis’ friends tell the Times that the defense secretary doesn’t want the military to be seen as a political tool. He avoids interviews so he won’t be seen publicly disagreeing with Trump, but he’s not willing to lavish Trump with praise.

That seems to be a problem for Trump, who’s made it clear that loyalty is crucial in his administration.