Jimmy McCain, son of the late Republican Senator John McCain, is endorsing Vice-President Kamala Harris following controversy around Donald Trump’s recent visit to Arlington National Cemetery.
He called Trump’s visit last week to the military burial site “a violation”.
The Army has accused a Trump staffer of pushing aside an Arlington employee as they tried to warn his team about rules against filming in the cemetery.
The Trump campaign says it received permission from families of fallen service members to film video during an event to honour US soldiers killed during the American withdrawal from Afghanistan in 2021.
“Show respect and leave. It doesn’t need to be videoed,” Mr McCain told CNN’s Jake Tapper on Tuesday.
He added: “The point of Arlington Cemetery is to go and show respect for the men and women who have given their lives to this country. When you make it political, you take away the respect of the people who are there.”
Mr McCain, who was previously an independent, said he has changed his voter registration to Democrat and plans to vote for Ms Harris for president in November.
“I feel that Kamala Harris and Tim Walz embody a group of people that will help make this country better. That will take us forward. That’s really what matters at the end of the day,” he said.
The youngest McCain son enlisted in the Marine Corps and has served as an intelligence officer since 2022.
Three generations of McCain family are buried at Arlington.
Federal law prevents use of the site for political campaigning.
The Trump campaign has disputed the cemetery’s version of events and released a statement from the Gold Star military families that invited him to the site, saying the former president was there to honour the sacrifice of their relatives who were killed.
Trump – who is running for president for a third time – and late Senator McCain had a long rivalry.
The Vietnam war hero was one of the most outspoken Republican critics of Trump from the very start of his first candidacy.
Trump once attacked McCain, himself a former Republican presidential candidate, saying he was “not a war hero” because he was captured and held as a prisoner of war.
In 2020, McCain’s widow, Cindy McCain, endorsed Joe Biden in his campaign to unseat Trump. Mr Biden later appointed her as US ambassador to a United Nations food agency.
Jimmy McCain is not the only family member to withhold support for Trump.
His sister Meghan said on Monday she does not plan to support either Trump or Ms Harris.
“I greatly respect the wide variety of political opinions of all of my family members and love them all very much,” she wrote on X, formerly Twitter.
“I however, remain a proud member of the Republican Party and hope for brighter days ahead.”