Basically, they're throwing in the towel. Lose with Biden/Harris in 2024 and then start fresh with a clean slate in 2028.
Trump is also done in 2028 and there’s no obvious successor unless Trump’s VP can step into his shoes.
The old saying is, you come for the king, you better not miss.
My guess is that they just called the party machine controlling Milwaukee, Detroit and Philadelphia, "no fraud this time" so they're not going to attempt to cheat in MI, PA and WI to defend the blue wall.
Knowing the Democrats, though, they might be accepting of a Trump victory now, but you can be sure they will oppose every move he makes in his new administration and will probably keep making up false scandals and criminal charges against his staff.