We know from his prior record he can "hire and fire"; his instincts as a competent leader enable him to do so when he has reason to believe a subordinate is irreversibly incompetent.
We also knew how motivated the Dems were to impeach him for even an imaginary misstep.
We, nor his team, did not know how many Rino's would be available to assist the Dems with their several attempts to impeach him.
We also do not know is what his "trusted and reliable" R inside advisors were recommending as to which were to be hired and fired and what kind of damage might the Dems been able to do in response.
It doesn't seem appropriate to pass judgment on any firing "failure" at this point, and until an insider writes a book we do not have the benefit of hindsight in this regard.
Fortunately, with the many things he accomplished while in office, I think it's clear Trump successfully served his apprenticeship as President.
You say, "Trump will need to clean house right away, without any hesitation lest the GOPe talk him out of it."
You are correct; and it will have to be a "deep cleaning".
The opposition will do everything possible to avoid completing that, but it's our nation's best option.
Jeff Sessions. William Barr.
Both monumental disastrous personnel decisions. Trump simply cannot allow people like that in key positions this time.
One weakness Trump has (nobody is perfect) is his huge ego. It appears that people can ingratiate themselves with him by flattery. We need fighters, not sycophants.
Its going to be hard for a one term limit president to attract good people to come into the DC Swamp and push his agenda. I hope he can successfully do that, but its going to be a real challenge for him.