Spiro Agnew's term of rebuke for the Democratic party in the 1970 elections.
The obits from September 1996 have the most recent coverage.
NewsHour with Jim Lehrer: Remembering Agnew
SPIRO AGNEW: In the United States today, we have more than our share of the nattering nabobs of negativism.
Time Magazine, 1996: Naysayer to the Nattering Nabobs
In a 1969 speech against war protesters, he said, "A spirit of national masochism prevails, encouraged by an effete corps of impudent snobs who characterize themselves as intellectuals." "In the United States today," Agnew told a 1970 audience in San Diego, "we have more than our share of the nattering nabobs of negativism." He went after "pusillanimous pussyfooters" and "vicars of vacillation" and "the hopeless, hysterical hypochondriacs of history."
Read more: http://www.time.com/time/magazine/article/0,9171,985217,00.html#ixzz0wY2gLHR5
The quote specifically from Bartleby, via the Congressional Record, pins it to the 1970 California Republication convention.
Vice President SPIRO T. AGNEW, address to the California Republican state convention, San Diego, California, September 11, 1970.—Congressional Record, September 16, 1970, vol. 116, p. 32017.
The original AP wire story is saved in Google News
Agnew's speech was prepared for a $125-a-plate Republican fund-raising dinner.
Edward Vielmetti's Wordpress weblog 
Too many people of faith think the world is going to hell in a hand-basket. What’s with hand-baskets anyway? Here’s my latest blog posting on why the Christians need to quit spreading the myth (through their constant complaining) that the world is just getting worse all the time.
http://accdocpastor.blogspot.com/2012/11/nattering-nabobs-of-negativism.html