Kerry’s issue was that he got awards for valor in combat, some of which do not appear to have been in combat, and purple hearts which also were either negligible scratches or did not occur in combat, and told a variety of stories about people in his squadron which were demonstrably not true. He wrote his own awards, as an officer, but they include claims of a combat for which he received a purple heart that allowed him to go home early, that in other narratives he told occurred before he had ever faced combat.
It wasn’t that some guys came out against him, it was that no one in his squadron not in his boat and not rewarded by him supported anything of consequence he said - though some things he said even his crew agreed were not true.
Kerry also made a big deal about blaming Nixon for sending him to Cambodia in 1968 and then lying about it on TV, yet that was before Nixon was President. Johnson was.
I agree with you about Kerry lying about Cambodia. Do you have a source for nobody in his unit on his boat vouched for him? My sources say only one member of the crew spoke against him.