I think the use of Big Mike is a real option for the Dems. Wrecking Ball Joe will not stand up down the stretch. I doubt he will be willing to debate Trump or Big Mike. Should Big Mike jump in, Wrecking Ball Joe proceeds to lose one primary after another.
Her/his message will be that we need a younger generation to lead the country. And that a Trump presidency would mean the end of democracy. All but 4 % of the blacks would vote for her, and 88% of the Hispanic vote would go her way, and white suburban women would run about saying it is time for a woman POTUS and vote for her. Trump would not know what hit him!!!