Former President Barack Obama’s campaign manager, David Plouffe, knows something about bad debate performances. Plouffe was one of the senior Obama officials in 2012 who broke the news to the president that he bombed in the debate against Mitt Romney. And now Plouffe is sounding the alarm on Joe Biden after the first of two debates against Donald Trump. “It’s kind of a DEFCON 1 moment,” Plouffe said after the event on MSNBC. “I’ve been deeply involved in presidential campaign debates. Some went well, some didn’t go well. The only thing that matters, and you won’t really know for three or four …