Remember, we’re talking about what the “final straw” is that broke the camel’s back.
Nah, though. We're not.
Howard Dean was squeaky clean when "the scream" happened. He was everyone's favorite, and it was too early to say for sure at that moment but we felt like he could win the whole shebang. Then he screamed and it came crashing down. It wasn't a "final straw". It was the only straw. A straw made of Republican propaganda and enemy action, swallowed by democratic liberals.
As for Jeb Bush, he was underwhelming from the start. Nobody wanted him to be president; probably not even him. "Please clap" was his admission that his campaign wasn't working at all. Again, not a final straw. In this case there wasn't even a camel in the room, just Jeb, giving up.
None of these models applies cleanly to Trump. It's not a "final straw" because there's a mountain of straw; bales of straw as far as the eye can see. It's not Howard Dean for the same reason. It's not Jeb Bush either, because Trump may be faltering but he is literally incapable of throwing in the towel. He doesn't even contain that, as an option.
So I don't know why this one is sticking, but I think we're closer to Jeb Bush territory than Howard Dean. I think everyone but Trump is getting a glimpse of the fact that this is going to be a bloodbath for him.