6:37 PM PT -- Donald Trump Jr. just threw some major shade at Avenatti at his father's political rally in Michigan, joking that Michael's presidential ambitions took a serious hit this week.

Junior jokes that Michael went from "Avenatti 2020 to Avenatti 20 to 25" ... clearly hoping his foe is going to prison for his role in the alleged extortion plot.

Michael Avenatti was loaded for bear Wednesday night, proclaiming his innocence in the extortion case, proclaiming that the R. Kelly case would be unaffected by the extortion case and proclaiming it's only a matter of time before top Nike execs would be led away in handcuffs.

We got the embattled celeb attorney in WeHo Wednesday night ... and we strolled along with him on a long, long walk ... where he unpacked his outrage.

Avenatti said all the talk that his indictment will torpedo the R. Kelly prosecution is BS ... because the evidence is the evidence is the evidence.

And then, he talked Nike. As you know, he's been accused of trying to extort the shoe co. for more than $20 million in return for keeping his silence on alleged misdeeds -- specifically, Nike secretly paid off the families of star high school basketball players in order to direct them to Nike-sponsored colleges.

He goes after Nike execs with a vengeance, saying they are corrupt to the core and it will be exposed. He also insists any money he may have demanded was not a quid pro quo for his silence. Avenatti says he was going to expose Nike regardless of whether the company paid him or not.

The U.S. Attorney claims he has a videotape from a March 21 meeting between Avenatti and Nike attorneys in which he allegedly says, "If [Nike] wants to have one confidential settlement and we're done, they can buy that for $22.5 million and we're done."