Of course Donald Trump will not debate against Bernie Sanders. Hillary Clinton would merely laugh at him. But Sanders would mix that with going very, very hard. It would be glorious to watch.
With Clinton, Trump just intends to bloviate about the menopause or what have you. But what would he say to Sanders, who has been arguing against neoliberalism and neoconservatism in great detail forever?
This is a Presidential Election without a Republican candidate, as such. Trump is effectively an Independent, as of course he can afford to be. The party refuses to have anything to do with him.
Likewise, his only connection to it is that he is going to take down numerous of its candidates for other offices, and not least for both Houses of Congress, along with him in November.
Of course, unlike Clinton, Sanders beats him in every national and state poll. If Sanders won the California primary, or even came close, then all bets would be off.
Trump would have been on the ballot with or without the Republican Party, and is, for all practical purposes, on the ballot without it.
Likewise, it is looking more and more as if Sanders is going to be on the ballot with or without the Democratic Party.
But quite conceivably with it.