President Obama's war on whistleblowers is generally an attempt to silence the stories that present the US in an unflattering (though true) light. Just mentioning this in case anyone thinks that Franken's quote indicates that the mainstream left actually shares Chomsky's principled stance.
Obama is not "mainstream left" or any other kind of left. He's best characterized as a moderate conservative. In Canada, where I live, Obama's beliefs would be considered to the right of our Conservative Party, which is considerably to the right of the Canadian mainstream but managed to win the last election because the centre and centre-left votes were split among three or four parties.