Yeah, you'd have to be physically wide to make yourself look like McCarthy (maybe you could stuff some pillows into a suit and bring a prop like a "REDS IN HOLLYWOOD" picket sign or a little badge). If you'd like the extra effort instead of putting on an old-timey politician hat, a bald cap with his hairline drawn onto it would add some extra definition to the outfit.
I would definitely need to stuff pillows and stuff into a suit, as I am quite lanky now. I bet I already have a big enough suit to use, though. I have a lot of suits laying around