“People don’t mind a politician’s hand-shaking and back-slapping, so much as his leg-pulling” was cited in several American newspapers in May 1935. Authorship is unknown.
 
Hal Cochran’s syndicated “Barbs” newspaper column published in 1952:
 
“A politician’s back-slapping and hand-shaking is usually spoiled by leg-pulling.”
   
     
13 May 1935, Piqua (OH) Daily Call, “Barbs,” pg. 4, col. 8:
People don’t mind a politician’s hand-shaking and back-slapping, so much as his leg-pulling.
 
13 May 1935, Kokomo (IN) Tribune, “Barbs,” pg 4, col. 4:
People don’t mind a politician’s hand-shaking and back-slapping, so much as his leg-pulling.
 
14 May 1935, Morning Advocate (Baton Rouge, LA), pg. 4, col. 2:
People don’t mind a politician’s hand-shaking and back-slapping, so much as his leg-pulling.
 
13 April 1949, De Kalb (IL) Daily Chronicle, “The Notions Counter,” pg. 4, col. 2:
It isn’t so bad, the politician’s back-slapping and hand-shaking, if it wasn’t for the leg-pulling.
 
Google News Archive
2 April 1952, Victoria (TX) Advocate, “Barbs” by Hal Cochran, pg. 6, col. 4:
A politician’s back-slapping and hand-shaking is usually spoiled by leg-pulling.
 
8 April 1952, The News (Frederick, MD)< "Greetings," pg. 1, left masthead:

Back-slapping and hand-shaking often lead to leg-pulling.
 
20 September 1956, THe Progress-Index (Petersburg-Colonial Heights, VA), “Barbs” by Hal Cochran, pg. 4, col. 7:
Back-slapping, hand-shaking and leg-pulling, from now until election.