He was elected, after all, by more than half of the american voters.
This common refrain does a lot of heavy lifting by assuming that Trump did not cheat to win (again).
I'm not saying he did, and him even coming close to being in office a second time is still a damning indictment of our society regardless, but the fact of the matter is that Trump had every incentive to do so (avoiding an almost certain prison sentence, plus multiple other lawsuits that could add on to it) and nobody bothered to challenge the results in the months after the election when Democrats still held power, so we'll never know the truth (since records of any misconduct would have likely been destroyed by now).