Even in 2008, it was obvious Clinton was the DNC’s preferred candidate and DNC still had their thumb on the scale. Despite this, Obama still managed to come out ahead. And with a base that was actually excited about their chosen candidate, they turned out to vote and Obama won.
The only lesson the DNC learned from this is that they needed to push their thumb harder on the scales the next time around.
Regardless of what Biden has done for the average American, his approval rating has been really bad for a while now. It may not be right or fair, but that’s what it is.
Despite Harris not actually being the incumbent, the Republicans managed to associate her with Biden and she more or less embraced it. Then the Republicans were able to frame themselves as the challenger to an unpopular incumbent president and it’s not surprising they did well.
Of course, it didn’t help either that Harris is the VP either. Perhaps if we had a primary and managed to pick another candidate that could distance themselves a bit better from Biden things would be different.
Go look at the numbers, particularly Georgia, Wisconsin, and Arizona. Biden won those states, but by a razor thin margin. If he had lost those states, he wouldn’t have won the electoral college. It would have taken less than 50,000 votes in those states flipping to Trump to change the outcome of the 2020 election.
Of course, that’s just the electoral college. Biden won the popular vote by a pretty comfortable margin.