Of course the Theory of Evolution is a fact; it's existential. It exists and anyone can read it and everything and all manners of things supporting/about it, and one can read it in all its vast detail or read a brief summary of it (though doing the latter hardly positions one to refute it). It doesn't matter whether one accepts it as an accurate depiction of how life evolved/evolves.
To be sure, the Theory of Evolution as Darwin presented it has itself been refined since Darwin's day; thus merely reading
On the Origin of Species isn't going to do the trick, as it were, for making one fully informed on the matter.
How Darwin envisioned evolution
The Integral Model of Evolution (the most recent refinement of the idea)
I wonder about that question, especially does Donald Trump think evolution is a fact ?
As for what Republicans think about the Theory of Evolution, well, I have no way to say credibly what they think. For all I know, they perceive it to be every bit as linear a thing as Darwin did. Hell, I don't know even whether most of them who'd refute it's validity have even read so much as the documents cited above, to say nothing of many or most of the myriad others that support (scientifically and with sound reasoning, not merely judgmentally) the Theory, so as to position themselves to be in legitimate mental state of comprehensive understanding about it to in turn refute it. Moreover, I don't know whether Republicans on the whole are fully aware of how the Scientific Method works.
As for what Trump thinks about the Theory of Evolution, well, I'll just say that as goes math and science (natural or social), the guy doesn't strike me as being anything even close to a prolific reader of rigorously developed content pertaining to those disciplines. But for his being POTUS, nobody would care what he thinks or might have to say about the Theory of Evolution. That he is POTUS doesn't make what he has to say any more meritorious; however, his being so can make his statements ominous, depending on what he says.