Ladies and gentlemen, please rise for the President of the Un ... BILL MURRAY! 

Bill took over the podium in the White House's press briefing room on Friday -- but instead of talking politics, he was all about the NLCS ... and explained why the Dodgers are doomed. 

Oh yeah, he happens to be a HUGE Chicago Cubs fan -- hence the pullover -- and warned Clayton Kershaw that his boys from Chi-Town are just too dominant for him.

It's funny stuff ... Hail to the Ghostbuster.