I don't know what Ferguson's personal politics are but like most people who make a living cosying up to the Hollywood leftist elite, he sure does give them aid and comfort.
I watch Letterman from time to time because he makes me laugh. But I would never, ever take his side if he got into a pissing match with a true conservative just because he entertains me. I think that would be pretty shallow.
Ferguson does not appear to be a leftist to me.