So if the president says "The sun won't rise tomorrow", we can't reject that statement out of hand?

Easy. A "statement" can't be wrong, but a "prediction" of the future must be built on a predictive model that has worked in the past, and the model must be fed parameters rooted in reality. Failing that, it is wrong.

If Trump's statement about fraud is not predictive, then it is fiction and meaningless instead of wrong.

Tomorrow gravity is going to reverse and fling you into the sun.

I don't know what that even means.

We're talking about facts established by research, indicating they have occurred in the past. I don't know what you're talking about.

You wait long enough and then check whether the prediction was true? If not, the prediction was false.