Over and over again, the defense espoused by those in official position is that "no one has done anything improper," because even if they were dismissed for the most blatantly improper political reason - to interfere with ongoing investigations of the corrupt Republican power structure in Washington - that wouldn't be improper because of of the Theory of the Unitary Executive, where the President has sole control over anyone in the executive department. This is an assault on the underlying conventions of our political system - that people are treated equally under the law. By changing the conventions without notice, they are turning this country into something it has never been.
So, there was political pressure, but that's entirely proper because the President has complete unitary authority over the executive. It's all part of the same slide.