(FILES) US President Barack Obama is seen with host Jay Leno during a taping of "The Tonight Show" at NBC studios in Burbank, California, on March 19, 2009. America's late night talk shows once were appointment viewing, but with ratings tanking and ad revenues plummeting, their coveted place on the small screen is in question. The hosts of yesterday and today -- comedians from Johnny Carson and Jay Leno to Jimmy Fallon and Jon Stewart -- are household names, and their jokes were once mandatory conversation starters at the water cooler. (Photo by Mandel NGAN / AFP) (Photo by MANDEL NGAN/AFP via Getty Images)