Who’s laughing now? Neilsen ratings released Friday say an estimated 51.4 million Americans tuned in to watch incumbent Joe Biden and vice-presidential hopeful Paul Ryan Thursday. The number is down significantly from 2008, when 69.9 million watched Biden battle it out with Alaska governor Sarah Palin. The executive director of the Commission on Presidential Debates, Janet Brown, told Politico that the inflated number of viewers in 2008 was an “aberration” likely due to excitement surrounding Palin's candidacy. Nielsen's numbers are based on total viewership on 10 major TV networks, excluding those watching online.