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That's my take as well -- Rogan's entire brand is that he'll have any guest who's interesting on the show, and there's no way he'd turn down the chance to have Harris if it came up.
And similarly, no way he'd agree (for Harris or Trump) not to ask hard questions. He'd lose his entire rep.
I'm not always a big Rogan fan -- there are times when he is a bit too credulous with some guests -- but while he'd be polite, he definitely wouldn't roll over for either candidate.