Campaign remark, Fresno, Cal., 10 Sept. 1952. John F. Parker, in "If Elected, I Promise ...": Stories and Gems of Wisdom by and About Politicians (1969), attributes the reverse statement to Chauncey Depew (1834 - 1928): "If you will refrain from telling any lies about the Republican party, I'll promise not to tell the truth about the Democrats."
Will Rogers, Bryan B. Sterling (1995). “Will Rogers Speaks: Over 1,000 Timeless Quotations for Public Speakers (writers, Politicians, Comedians, Browsers ...)”, M Evans & Company
Speech at Loyola College Alumni Banquet, Baltimore, Maryland, on February 18, 1958. "John F. Kennedy Quotations: Profiles in Courage Quotations", www.jfklibrary.org.