Election experts are split on whether voters today are most motivated by positive excitement (I love my candidate and want him/her in charge because I think they'll do a great job) or negative excitement (I detest the opposition, they symbolize all that's wrong with the world and I support anyone who isn't them). Candidates and their campaign teams go back and forth on whether it's more important to put out a positive message about themselves or to portray their opponent negatively. In the end, they usually split the difference and try to do some of both--but it's long been a question of which type of campaigning is more effective per dollar to win an election.
And you may say that if Biden won due to negative excitement, he's in trouble for 2024 because (most likely) Trump won't be his opponent. But every year, the nation grows more tribal and polarized, which makes voters amenable to the idea that whomever is the candidate of the opposing party is awful.
If I were to guess, I would say that positive excitement has generally been more important to Democratic candidates and negative excitement has generally been more important to Republican candidates. Those on the left tend to be more idealistic and want to believe in something and a leader who evokes those ideals. Republicans (as conservatives) have generally brought the message that change is risky and radical change is frightening and potentially devastating. That's where the famous saying, "The left falls in love while the right falls in line" comes from. From an electoral standpoint (and arguably from a philosophical standpoint, though it depends on what you value), this can be seen as a knock on both sides.
However, I think that's changing. I think the era of intense polarization and the confrontational nature of a social media driven Internet has caused both sides to focus more on anger and dislike of the other side, left or right. Politics these days is about anger.
