Part of the problem is that the Democrats also need to think long and hard about who they serve. Trump should have been *impossible*. In a healthy country nobody would have voted for a raging whackadoodle like him.
The problem is well, the non-Republican voters. Democrats win or lose by voter turnout - it's why the (R) side is trying to disenfranchise as many voters as possible.
You see, the voter turnout for the (R) side is basically constant - you have people who vote (R) and will always vote (R) every election. Doesn't matter who's on the ticket, as long as it's (R) it's who they vote for.
On the (D) side, it's a lot more variable - they are generally far more complacent. If they don't like who's on the ticket, they don't show up to vote.
Granted, there are small contingents of flip-flop voters - but in the overall scheme of things they don't usually matter too much. Sure they may have flipped a state, but it's debatable in the end if it mattered.(E.g., the LatinX vote went (R) in 2024, because they liked the whole "close the border" thing and "get rid of the immigrants". But of course, they didn't think things through because well, they were the immigrants).
So what matters in the end is the voting contingent - you have (R) when the (D)s don't vote. It's why talk of forcing voters to vote has died down - the (R)s realized that it was a completely bad idea that would have them lose the election because you're forcing basically the (D)s to come out to vote. That's also why there's talk of "steal the vote" and "voter ID" - because the goal is to make sure the (D)s don't vote.
(Incidentally, you can't be for things like "voter ID" and then believe the times when Trump was in power the vote was proper. Because it was improper in the past and thus the 2020 was stolen by Biden, but also 2016 and 2024 was stolen by Trump and thus every one of them was illegitimate without voter ID. Which we all know wasn't true, because the MAGA tried to steal the vote in California and failed miserably to the point of almost getting arrested for trying it. So either you need voter ID, and thus the vote for Trump was also illegitimate, or you don't, and Trump is rightfully the President.
That's really what it boiled down to. Bust Jr. was elected because Gore lost Florida because of potentially uncounted votes.
In the end, all that matters is getting the vote out. All the (D)s though Kamala Harris had it in the bag and stayed home. It's why if anyone claims "they don't bother to vote" or "I don't care" your answer is "so you voted for Trump then". Not voting is the same voting for the winner - if you wanted Harris to win, you'd have gone and voted. If you didn't care, you basically voted for Trump.