In the McGovern chapter of Almost President: The Men Who Lost The Race But Changed The Nation, the book describes how Richard Nixon tried to paint George McGovern as a coward who refused to fly a particular mission and that McGovern had earned the Distinguished Flying Cross and flown 35 B-24 missions over Italy.
WI McGovern used his war record as a club against Nixon? IIRC during WWII, Nixon visited the Pacific and made some logistics reforms or something like that, but did not see combat.
McGovern harped a lot about how evil the Vietnam War was and annoyed people by claiming THEY were responsible for it, but depicting Nixon as a "chickenhawk" in contrast to him who has seen war and knows how horrible it is might cause him major problems.