The thing that people around Trump keep stressing is how small his circle is. There's Kellyanne Conway, Mulvaney, Dan Scavino, Kushner, Parscale, Ronna M, Sekulow. Within the Cabinet, Barr has been someone described as someone Trump relies on. But that's about it.
Mulvaney is basically left with few allies at a top level right now. So he went out to the briefing room at a moment when he needed to show POTUS he could do the job. And it didn't go well.
I missed a few, as @KateBennett_DC noted - including FLOTUS, Grisham, Pompeo. But basic point that it’s a small group now is the same.
And Pence.
