There is no doubt to me that, for example, Ted Kennedy thought Leftists to be stupid. Jimmy Carter probably thought they were intelligent. Ronald Reagan treated them kindly, though the opposite was certainly not true. Stupidity and the Left has a long and bloodied history, and all the historical evidence is there.
Jonathan Gruber is only saying out loud what the leftist elitists have been saying quietly about their followers for years. Lyndon Johnson certainly understood that, and so does Barrack Obama.