I'm picking a bit on headlines here instead of the stories themselves but any time you're arguing "candidate X can't win the election", you're doing it wrong. We don't know that much about electability and what we do know suggests differences in candidates don't matter THAT much.
In principle, if you want to argue say Candidate X has a 55% chance of beating Trump and Candidate Y has a 35% chance, that's at least a plausible magnitude for electability differences. Though in practice, it's hard/impossible to be that precise 10 months in advance, of course.
Any of [Biden, Sanders, Warren, Buttigieg, Klobuchar, Bloomberg, etc.] can beat Trump. And any of them can lose to Trump. If you think otherwise, you're extremely overconfident about how much is knowable about any of this.
