WASHINGTON — 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.”
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.
Her support for the former vice president, who she recalled introduced her to Mr. McCain on a congressional delegation trip over 40 years ago, was not surprising, given her husband’s frequent clashes with Mr. Trump. However, Ms. McCain’s full-throated endorsement and her willingness to stump on Mr. Biden’s behalf illustrated how much the articles about Mr. Trump’s disregard for veterans, which he denies, stung military families.
Some of those reports, including the original revelations in The Atlantic, also detailed Mr. Trump’s contempt for Mr. McCain. After Mr. McCain’s death in 2018, the magazine reported citing unidentified people, Mr. Trump grew angry seeing that flags were at half-staff, saying, “We’re not going to support that loser’s funeral.”
Asked whether she had considered Mr. Trump’s reaction to her endorsement of Mr. Biden, Ms. McCain said she would just “laugh it off” if the president attacked her in one of his “5 in the morning” tweets.
She may have the most impact in her native Arizona, where her family has long owned a beer distributorship and which Mr. McCain represented in Congress for 35 years.
Mr. Biden has been competing more aggressively in the state than any other recent Democratic presidential nominee and has led in every reputable poll of the state, which has not backed a Democratic candidate for president since 1996. The former vice president now enjoys the public support of an array of prominent current and former Arizona Republicans, including former Senator Jeff Flake and former Representative Jim Kolbe, who long represented the state in Congress, and the onetime state attorney general Grant Woods.
If Arizona flips this year, it would greatly complicate Mr. Trump’s electoral map, given his current difficulties in the industrial Midwestern states he narrowly carried four years ago.
Democrats could also pick up the Senate seat in Arizona that Mr. McCain long held and is now held by Senator Martha McSally, who was appointed to replace him.
Ms. McSally has sought to straddle the more moderate McCain wing of the Arizona Republican Party and the hard-line supporters of Mr. Trump. But her refusal to defend Mr. McCain more vociferously in the face of Mr. Trump’s attacks, which he has kept up even in recent weeks, has angered the McCain family.
Ms. McCain, asked whether she would support Ms. McSally, who has consistently trailed in the polls behind Mark Kelly, the Democratic challenger, flatly said no. “I have no interest in it,” she said.