From Thirteen Days
At this moment the president is accepting the terms of Secretary Khrushchev's letter of Friday night: If the Soviet Union halts construction immediately, removes the missiles, and submits to UN inspection, the United States will pledge to never invade Cuba, or aid others in that enterprise.
If your Jupiter missiles in Turkey were removed also, such an accommodation could be reached.
That's not possible. The United States cannot agree to such terms under threat. Any belief to the contrary was in error.