Kerry bragged about his military service so much while running for office, of course people would take notice and look into it.
And, big surprise, they found that
A) Kerry's Purple Heart injury was self- inflicted.
B) Kerry afterwards led a bunch of anti- war protests in which he called his fellow Vietnam veterans "War criminals" and threw his medals (The ones he kept bragging about when running for President) at the White House steps.
C) He met several times in France with the leader of the Viet Cong, who helped directly orchestrate several of the anti- war protests he led, including the medal- throwing one, in the hopes of undermining America's support of the Vietnam War. Last time I checked, deliberately corroborating with our nation's enemies for the specific purpose of undermining our country is what's known as "High treason."