I don't know about "starting to." His competition was Jeb! Bush, Hillary, and Kamala. These were all people that thought they can coast to victory and not go on the campaign trail in swing states and convince non-Partisans to vote for them. They didn't speak on how to fix current issues or explain why they are better than Trump. They also didn't do their oppositional research very well and flooded it with complete nonsense, which is why Russiagate was a massive waste of everyone's time. Dems didn't argue the merits or lack thereof of Trump's policies and explain why they're bad or unworkable, they just opposed everything because Trump said it. Hence their total flip-flopping on COVID.
Even now, when they've got the perfect reason to oppose Trump, they still approve of his biggest blunder; the Iran War. Even if the Dems win, they're terrible on energy policy and will not fix rising gas prices. More US refineries will shut down, as we can see with California, the state that is run by the Dems with zero opposition. Now, sure it is possible that Dems sort their shit out, but that's hard work and as
@Althalus points out, a lot of it.