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."
Speech at Loyola College Alumni Banquet, Baltimore, Maryland, on February 18, 1958. "John F. Kennedy Quotations: Profiles in Courage Quotations", www.jfklibrary.org.
Will Rogers, Bryan B. Sterling (1995). “Will Rogers Speaks: Over 1,000 Timeless Quotations for Public Speakers (writers, Politicians, Comedians, Browsers ...)”, M Evans & Company