Pat...I have no doubt he IS passionate, but I really think his brain works so fast his mouth is trying valiantly to keep up and he ends up replying to himself as others try to answer.
He really does seem to thrive on those who slip in an "I agree with you, Chris.." as part of their reply.

I know a couple of people whose brains churn out various 'output' in similar ways, but they aren't on national TV. It is simply hard for them to restrain the impulse to say almost everything they are thinking. Matthews at least has 'partial' control over the flow, else he'd not be able to function in his job at all.

(and I think that Sherrod Brown is one of the few bright spots in Ohio politics)