Final answer:
John F. Kennedy's service as a World War II Navy veteran was not a challenge to his ethos for many Americans, in contrast to concerns about his age and Roman Catholic faith.
Step-by-step explanation:
The challenge to John F. Kennedy's ethos for many Americans that was not a concern was His being a World War II Navy veteran. Kennedy’s service in the Navy and the heroics he displayed in saving the crew of his PT boat bolstered his reputation and greatly contributed to his appeal during his political campaigns. In contrast, his challenges included concerns over his youth, as many saw him as too inexperienced at the youthful age of 43 to lead the nation. Furthermore, some Americans viewed his Roman Catholic faith as a potential issue, fearing his decisions would be influenced by the Pope. This was despite being the first Catholic to be elected President of the U.S., which in itself was a groundbreaking event.