Thanks @TQ for the request!
  1. William McKinley
    I'm not sure that he saw them himself, but it's possible, because according to "Red, White and Blaine" (as shown in the feature mockumentary "Waiting for Guffman"), both President McKinley and aliens made visits to the fictional Blaine, Mo., in the town's short history. I'm sure an ET sighting would've knocked him right back on his stool.
  2. Dwight Eisenhower
    If you believe a Daily Mail story quoting a former government contractor, who claimed a few years ago that Ike took three meetings in 1954 with aliens as the result of telepathic messages transmitted by the Pentagon. I refuse to link to The Daily Mail but you can Google it.
  3. George H. W. Bush and Ronald Reagan
    In 1980, "illegal aliens" was still a term, but both Republican primary candidates agreed they should be treated with compassion and that fences were silly. Please watch this:
  4. Jimmy Carter reported seeing an UFO in Leary, Georgia, 1969. While he was governor of Georgia, Carter was asked to file a report of the sighting by the International UFO Bureau in Oklahoma City in September 1973.
    Suggested by   @mjprovine