I think it is very strange that the same media that for years thought his gaffes were amusing turned on him so rapidly after the debate. He didn’t change overnight. They have been covering for him for years. So what changed? Maybe there is someone waiting in the wings who didn’t want to do a messy primary? Maybe that was the plan all along? Don’t know...but something doesn’t seem right!
What changed is that all of a sudden the whole country saw on live TV just how bad he had gotten.
I think the MSM hacks really believed that by giving him the questions he would get ahead of time and surprising Trump with hardball questions they could make Biden look good enough so they could keep covering for him up until the election. Remember every one of them is an anti-Trumper. They knew he was not ever going to last 4 years but would rather have a succubus -- Kamala Roundheels -- than DJT.
But after the entire world saw that "debate" they knew the game was over. And they all at once ran for the exit, hoping to make us believe they had been fooled as much as we were. Of course we knew they were in on the charade all along, but a lot of dems are gullible enough to believe them.
Throw in the fact that every dem contender knows that in 2028 there will be no incumbent running, and no strong candidate is willing to take any chances in 2020.