Not saying that it is impossible for Trump to win, but suggesting that 2016 is indicative of his chances in 2024 may be problematic for a few reasons:
- His opponent (Clinton) was someone who had been subject to character assassination for over a decade. (I know republicans will try to paint all Democrats as "commie-socialists", but I think the attacks on Clinton were much more significant than against most potential Democratic candidates)
- His lack of political history in 2016 allowed people to make favorable assumptions about how he would govern. (He was actually seen as more of a moderate than Clinton was in the 2016 election, and many of his promises were vague enough that people could read in almost anything into them.) After 4 years though, we know exactly what he is like.... he didn't become "more presidential" after the election, and he was more interested in tax cuts than improving health care. And lets face it, he left office when the economy was struggling.
- Democrats/the media/etc. are more aware of the risks of having him back in power. (In 2016, left-wing voters might have decided to sit things out or vote 3rd party, thinking "Clinton has this in the bag/what harm could Trump do". Now, they will be more likely to rally around the Democratic candidate as the best way to keep Trump out of office. And in 2016, the media was treating him with kid gloves, which will be less likely to happen now.)