Trump’s biggest mistake is that he did not clean house at the top 3 to 4 levels of government and put in people who would clean house of the rest of their organizations.
First, the rules do not allow a POTUS to make such deep changes in personnel.
Second, the people who were recommended to him were tainted. Look at how many cabinet officials he had to fire because they were loyal communist party members parading as Republicans.
Trump's best picks were from outside DC and politics and not from people advising him with long political careers.