President John F. Kennedy (1917-63), as we all know, did not serve even one full term in office. So if portraits of him were to be painted while President, there was less opportunity than usual.
On the other hand, Kennedy was the subject of thousands of photographs, and it is through these that we shape our visual image of the man. Those photographs also served as the basis for posthumous portrait paintings created by both professionals and amateurs. Below are examples of Kennedy portraits done by professionals. Some were painted while he was alive, others later. And some paintings done before his 22 November 1963 death might have been entirely photograph-based.
The Saturday Evening Post magazine would sometimes feature covers with paintings of presidential candidates in the weeks leading up to an election. The painting shown above was published in its 29 October 1960 issue. I don't know if Rockwell saw Kennedy in person while working up the image. He was able to spend an hour and a half with Dwight Eisenhower in 1952 in conjunction with a Post cover appearing before the voting that year.
This looks like it might have been done from life, but I have no solid proof.
This was probably done from life because it is known that Kennedy sat for her.
Also probably done from life.
Fuchs was an illustrator and not yet a fine-arts painter when he visited the White House to make sketches of the President. David Apatoff posted useful information about it here.
I have no information as to whether this was done before or after JFK's 1963 death. And if it was done before, I don't know if Greene did it from life.
I don't have a date for this, but it was probably painted on the basis of photographs and the sketches mentioned above.
This is the official White House portrait of Kennedy, painted years after he died.
I apologize for the information gaps noted in the captions above. If readers can supply facts regarding whether or not Kennedy actually sat for the unverified (in my remarks) portraits created in his lifetime, please let us know via a comment.