I believe Trump, but I only believe him because the messaging seems to be "nobody knows what I know". I believe him because "what everybody knows thus far" isn't doing him any favors.

The only evidence I've seen that would give any credence to election fraud is the data feed vote subtractions / irregularities, and the sworn testimonies from people alleging backroom / closed door adjudications. Neither of those things are actual evidence without further investigation.