This seems to vastly overestimate the amount of politically active people. How can there be 100 million people when only 130 million people voted in the last election—most of them against Trump?
This poll uses “voting Americans” of which there’s only about a 130 million total. So that 45% shouldn’t be surprising at all—Trump won 46.10% of the popular vote. It seems his base is still enthusiastic about him which doesn’t surprise me.