I am sorry to break it to you, but this happens all the time, and is not a violation of due process. You can find examples of many Presidents declaring opinions on the guilt or innocence of a variety of people before their trials. [1] It makes sense that this is allowed, as the Justice Department is a part of the Executive Branch, so all prosecutions are done with the tacit or explicit approval of the President. It would be more problematic if the judges in the case expressed views on guilt or innocence before hearing the case.
[1] https://www.commondreams.org/newswire/2011/04/25/obama-decla...
There's also an argument to be made for holding our political officers to a much higher standard than the general populace.
For one very obvious example, observe that it is illegal to notice an opium poppy is growing in a forest, then take and smoke it, and somehow that magically being interstate commerce.
At this point the government as we know it would totally collapse were it not the people willfully and deliberately violate the tenants of the constitutional republic we live under. And most of them, seem to agree with that.