Why did Trump fail?
He didn't fail. Was pretty much successful. Lost the election on razor thin margin, that was more like a toss than a decision. And that in the face of all major media declaring a landslide win for Biden which never materialized. No "Blue Wave."
Compare that with all the doubts everyone was having regarding Trump's presidency when he won the first term. He did excellent since; building a cult like support around him with 50% of the population.
Plus I strongly doubt Biden can run a second term either. His age.