He isn't. He is on the Half Dollar dollar because Congress thought he deserved the honor and rushed the enabling legislation through within weeks of his assassination and the first coins were minted within three months.
The president on the 50 cent coin is John F. Kennedy.
On the Kennedy half dollar
jfk kennedy coin july 1963 half dollar is priceless
The 50 cent piece.
The 50 cent coin.
The 35th President of the US, John F. Kennedy, is on the half dollar coin
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The John F Kennedy Inauguration coin is a silver coin that shows him taking the oath. His right hand is raised, just as it was when he was sworn in as president.
The 50 cent coin bears the head of President John F. Kennedy
John F. Kennedy January 20, 1961
John F. Kennedy, since 1964. From 1948 to 1963, Benjamin Franklin. Prior to that, various images of Miss Liberty.
John F Kennedy was a Democrat.