Tweet by tweet: John McCain and Donald Trump feuded for years. (Arizona Republic, 8/25/2018)
I'd call this more othan just a 'feud'.
July 18, 2015: The feud really exploded when Trump, at a Saturday event in Iowa, disparaged McCain's service during the Vietnam War. Trump, who did not serve in Vietnam, said McCain was “a war hero because he was captured” and that he liked “people that weren’t captured.” McCain, a former Navy aviator who was shot down in 1967 and held as a prisoner of war for more than five years, was defended by groups such as the Veterans of Foreign Wars, the Military Officers Association of America, Iraq and Afghanistan Veterans of America and Concerned Veterans for America.
No sincere apology was ever offered.
Sampling of other snipes