Does that mean you think these claims are foolish?
Don't you think it's weird to make political predictions, and then say such predictions are foolish?
Testability.
If Biden loses in November, is there anything you think we could measure, to try to determine what factors contributed to his loss, and whether depressed turnout among Bernie Bros vs other progressives was one of those factors?
To be clear: I'm not asking you to prove your prediction ahead of the event. I'm asking you if there's any way you can think of to measure the event when it happens, and see if your prediction was accurate.
I haven't made any such prediction. Bernie Bros have been threatening this for some time. Now you're predicting that the majority of Bernie supporters will turn out for Biden. Come November, can you think of any way to test this?