I guess you could say that the death started with Dick Cheney. His unprecedented level of power in a position that people would always joke about as being "useless" must have made the Dems decide on this "I need someone dumber" system that they've been doing, all because of how massively unpopular Cheney was upon his departure.
The main reason this went wrong for them is because Kamala Harris accidentally(?) become an incredibly powerful vice president as well. The 50/50 Senate effectively allowed her to pass/veto anything as she wanted with her tiebreaker votes (she's done 33 in total, which broke a "record" that had stood since 1832), as long as the number of "defectors" for each party remained equal. And, as for the actual "president" ...well, yeah.
There are few things more dangerous than an idiot in power. The crap we've went through in the past four years was a great example of this.