In his book Truman, David G. McCullough writes extensively about President Harry S. Truman's love for bourbon, in which he was joined by his wife Bess. He further writes that the President's preferred drink was Old Grand-Dad on the rocks.

Carson-Verzola Historical & Audio Archives --
American Presidents-Presidential candidates --Their Food & Drink Preferences & Dislikes--A fun Survey & Overview
Does Obama eat Pork--Hot Dogs or Ribs?

"Harry S.Truman: His favorite drink was bourbon. He reportedly had a glass in the morning for breakfast. President Truman was often fond of a glass of bourbon. His favorite brand was I.W. Harper. His wife, Bess, never knew that he kept a hidden stash of it in his personal bathroom."

Something he shared with 007 James Bond -
"Bond seems fond of two bourbons in particular ó Old Grand-Dad and I.W. Harper. Of the two, Harper is the harder to find in the United States, though if you happen to be in the middle of a You Only Live Twice adventure in Japan and donít feel in the mood for sake, youíre in luck."