I think that Joe could possibly challenge Trump in the general election. But the primary will be tough for two reasons.
He’s is part of the most despised demographic of the progressives. Old or middle aged white men are not in demand. He doesn’t look like someone that they value.
He doesn’t hate enough. He occasionally treats republicans as if they are actual human beings. The way politics used to be done. This is a mortal sin and he will need to be nastier if he wants to stand a chance. To get the nomination, a democrat must make no distinction between a republican and the Waffen SS. They need to be treated with equal contempt.
Rather than change to please the haters, Joe should keep his dignity and retire.