It gives Sanders at good chance of boosting his percentage in the Kalifornia primary. It also makes Hillary seem irrelevant. That will damage her.
She’s in a damned if she does, damned if she doesn’t position. Joining the debate sends the message that Sanders is still in the race which she and her media sycophants have been denying.
It’s a big lose, lose for Hillary. Losing relevancy is the kiss of death for a politician.
The only way uncle bernie can truly make bigger inroads in to Cali is if the kardouchians were to endorse Donald. BOOM!
A Trump-Bern ticket is an absolute, 100% guaranteed shoe-in for election. The only downside risk is that Trump doesn't make it the full 4 or 8 years. How much of a gambler are you & the country?
The same risk analysis holds true for Bern supporters: no chance of winning as a Dem, 100% chance as Trump's running mate. They're bet is the opposite ie Bern taking over, yet voting Trump-Bern at least makes it possible.
And if Hillary's 'in' it's two high IQ minds against a person who's only 'skill' was being the wife of a powerful man.
I see a slightly more insidious motive for Trump. This may be a stretch but here I go. Hillary was mortally wounded in the IG report. It is over for her. The Democrat party will not allow bernie to be the nominee. He is anti their establishment and he will get slaughtered by Trump. The Party will give her the nomination but she will resign based on poor health and her “grand child” needs her. Obama will grant her pre indictment clemency . Since the convention has been held, there will be a special “closed” convention of State “designates”. No press or cameras!! . Bernie will go wild but the nominee will shock you. Trump wants to build up bernie as much as he can to accentuate this trickery on bernie and infuriate his communist followers. The “debate” will be fun to watch . Trump will bait bernie on how he has been screwed. Its all a plan.