“The trouble with political jokes is that they get elected to office” is a quote frequently attributed to Henry Cate VII, but he appears simply to be a 1990s contributor to rec.humor. The phrase is cited from 1958 and is attributed there by nightlife columnist Earl Wilson to actor Tony Pettito.
 
Former New York State Governor Eliot Spitzer—who resigned in disgrace after it was revealed that he visited with prostitutes—had this statement in his 1977 Horace Mann High School yearbook: ““The worst thing about political jokes is that some of them get elected.”
   
     
6 August 1958, Uniontown (PA) Morning Herald, “It happened last Night” by Earl Wilson, pg. 4, col. 2:
EARL’S PEARLS: “The trouble with political jokes,” says Tony Pettito, “is that they get elected to office.”
 
23 October 1958, Ada (OK) Weekly News, pg. 4, col. 4:
The trouble with political jokes is that they often get elected to office.
—Tony Pettito
 
3 July 1960, Zanesville (OH) Times Recorder, “Main Stem” by Bud Harsh, pg. 6:
The Main Stem Philosopher opines:
“The trouble with political jokes is that they sometimes get elected to office.”
 
8 November 1960, Charleston (WV) Gazette, George Lawless’ “The Gazetteer,” section 2, pg. 13, col. 1:
The trouble with most political jokes is they usually get elected.
   
3 December 1961, Hartford (CT) Courant, “The TV News Beat” by Hank Brant, pg. 14G:   
Reason why Jack Benny won t tell political jokes: “The trouble with most political jokes is that they sometimes get elected!”
 
Google Books
Lifetime Speaker’s Encyclopedia, Volume 1
By Jacob Morton Braude
Englewood Cliffs, NJ: Prentice-Hall
1962
Pg. 604:
The trouble with political jokes is that they often get elected to office.
 
9 November 1968. Colorado Springs (CO) Gazette Telegraph, “Bradley Broadly” by Wes Bradley, pg. 23C, col. 2:
SHE: Do you know any Political jokes?
HE: Know any? I voted for three of them.
     
22 September 1976, Charleston (WV)

, pg. 3B, col. 3:
It would probably be wise if President Jerry and Mr. Peanut forget about political jokes. American voters know too many political jokes get elected nowadays.
   
The Empire Zone Blog - NYTimes.com
November 29, 2006, 6:20 pm
Blogtalk
By THE NEW YORK TIMES
Eliot Spitzer’s favorite quotes, from his 1977 Horace Mann yearbook, including this one: “The worst thing about political jokes is some of them get elected.” [The Daily Politics.]
 
Barry Popik tracks down “anonymous.” [Room 8]
     
Wall Street Folly
Eliot Spitzer hooker scandal irony: “The worst thing about political jokes is that some of them get elected”
March 11, 2008
Here’s a picture of Eliot Spitzer from the 1977 Horace Mann High School yearbook that Stock Market Prognosticator, who was a few classes behind him, posted and pointed us to.  Look at the quote that we’ve highlighted in yellow from Eliot Spitzer’s entry.
 
“The worst thing about political jokes is that some of them get elected”