Cindy McCain, the widow of Senator John McCain of Arizona, formally endorsed Joseph R. Biden Jr. for president on Tuesday, praising the “character and integrity” of her late husband’s longtime friend and colleague while voicing her unease with President Trump.
Ms. McCain, who spoke in a video at the Democratic convention last month, said in a telephone interview that she had been uncertain about how public a role she would play in this year’s campaign. But after reading reports this month that described Mr. Trump denigrating members of the military, she said, she became “more and more frustrated” with the president.
“The most important thing that moved me a great deal was talking about troops’ being ‘losers,’” Ms. McCain said, referring to an article in The Atlantic. “You know we have children in the military, as did the Bidens.”
She added, “I want my president to have my back, and I don’t believe that’s the case right now.”
Mr. Trump responded Wednesday morning with digs at both Mr. Biden and Mr. McCain. “Joe Biden was John McCain’s lapdog,” he wrote on Twitter. “So many BAD decisions on Endless Wars & the V.A., which I brought from a horror show to HIGH APPROVAL.”
The McCains’ two sons, Jack and James, both served in the armed forces, and Mr. Biden’s son Beau served in the National Guard, including a tour of duty in Iraq. Beau Biden died of brain cancer in 2015.
Ms. McCain said she was planning to actively help Mr. Biden and would participate in virtual campaign events and join him when he appears in Arizona, which is seen as a swing state this year.