The top Democrats have been flipping out since the debate, seeing their chances to win slipping away and finally being successful in pushing a very reluctant Joe Biden out of the 2024 race. They were losing in the polls with Biden, which is why they did it. It wasn't because they suddenly realized he was incoherent. It's all about holding onto control. They're all fearful of former President Donald Trump coming in, not because they really think he's a "threat to democracy" but because they fear he might actually start holding people accountable. So they threw Biden under the bus...