Mulvaney has been working on major guv downsizing proposals (that of course went nowhere in Congress) for years now. I would imagine he has worked out the mechanisms for getting them enforced internally. I am not aware of Trump still having overtly Never Trumper cabinet officials (Mrs. McConnell, the Chinese agent, of course has her spot still, but she doesn’t resist overtly) at this point either.
I believe Trump chose MulVaney as his Chief of Staff because of his experience at OMB. I’m trusting ‘the plan’