The New York City humor magazine Life published on June 28, 1923:
 
“THE presidential candidates have started roaring. But you should never judge presidential timber by its bark.”
 
“Never judge presidential timber by its bark” is an infrequently used political adage.
 
     
Google Books
28 June 1923, Life magazine, pg. 6, col. 2:
THE presidential candidates have started roaring. But you should never judge presidential timber by its bark.
 
16 June 1924, Rockford (IL) Republic, “Hit and Run,” pg. 6, col. 2:
You can always distinguish presidential timber by its bark, says Diogenes Dinkle, Whig Hill philosopher.
 
6 June 1968, Aberdeen (SD) American-News, “Earl Wilson’s New York,” pg. 4, col. 5:
EARL’S PEARLS: Here we go again, trying to judge presidential timber by its bark.—Ben Bergor, Wisconsin State Journal.
 
Google Books
20,000 Quips & Quotes
By Evan Esar
New York, NY: Barnes & Noble Books
1995, ©1968
Pg. 109:
Never judge Presidential timber by its bark.
 
11 December 1991, Los Angeles (CA) Times, pg. B10, col. 1:
Candidates
Never judge presidential timber by its bark!
HAROLD GOULD
Los Angeles
 
Twitter
Michael D Thornton
‏@mthorntoncpa
Mentioned to my Lib Dem friend that I think entirely too many people are judging Presidential timber by its bark these days… #tcot #humor
5:19 PM - 3 Aug 2012