Charles Lindbergh was one of the most well-known aviators in the world. After the attack on Pearl Harbor and the US entered WW2, Lindbergh sought to enlist and serve. But he was refused. Why? He was only ~40 years-old, an experienced pilot, and still young and healthy. I would have thought that he would have been allowed to at least serve as an instructor pilot. Or, at the very least, some sort of public relations officer as many other celebrities did. Why was he refused?
His previous friendliness with the Nazis and supportive statements about them, and his support for the America First movement to keep the US out of WWII, among other things, made him a personal and political enemy of FDR, who blocked him.
Lest that sound like an anamoly, there were those inside the FDR administration and out (Joe Kennedy for example) who had similarly been friendly or even supportive of the Nazis prior to WWII, some toned it down when such things became officially a no-no after 1936, some did not and found themselves on the outs.
Ultimately, it was Lindbergh's very public political activism as part of the American First crowd (and his association with Henry Ford) that earned him the ire of FDR, as that was linked to the Republicans and political opposition to his administration and FDRs re-election /campaign for a third term.
Incidentally, Lindbergh ended up getting a contractor position in the Pacific and local units allowed him to fly combat missions (as a civilian). When FDR became aware of it, Lindbergh was recalled back to the US and eventually went to work in the defense industry.
Source: Nearly every biographer of Lindbergh covers this, but you may also find Lynne Olson's Those Angry Days: Roosevelt, Lindbergh, and America's Fight Over World War II, 1939-1941 to be illuminating.