▶ Watch Video: Democrats to formally nominate Joe Biden on second day of convention

Cindy McCain, widow of John McCain, the longtime Arizona senator and 2008 Republican presidential nominee, will appear in a Democratic convention video Tuesday night offering her support for Joe Biden.

McCain is the latest Republican to make an appearance at the virtual Democratic convention. On Monday night, four Republican leaders, including former Ohio Governor John Kasich, encouraged Republicans and independents to support Biden. Cindy McCain’s appearance is particularly notable, since her husband and Sarah Palin ran against President Obama and Biden in 2008.

A teaser for the video, titled “An Unlikely Friendship,” was posted by the Democratic National Convention Committee ahead of the start of the second night of speeches. John McCain and Biden met when McCain was assigned to be a military aide for Biden, then a Delaware senator. They became friends, and their families would picnic in the Bidens’ backyard.

“They would just sit and joke. It was like a comedy show, sometimes, to watch the two of them,” Cindy McCain said in the clip.

She is not expected to endorse Biden “at this time,” a source close to McCain confirmed to CBS News.

John McCain and Biden served in the Senate together for decades and formed a close relationship that lasted until the end of McCain’s life. He died of the same form of brain cancer that took the life of Biden’s eldest son, Beau Biden. Biden visited McCain shortly before he died in 2018, and afterward said that McCain had urged him not to “walk away” from politics. He was also a pallbearer at McCain’s funeral.

Cindy McCain said in 2019 that today’s Republican Party “is not the party that my husband and I belonged to” and rebuffed Mr. Trump. She has also said she thinks it’s possible Democrats will win Arizona this fall. Their daughter, Meghan McCain, is an outspoken critic of the president and has indicated that she may support Biden for president.

Mr. Trump often berated John McCain, saying during the 2016 presidential campaign that he liked soldiers who weren’t captured. As president, Mr. Trump continued to disparage McCain, whose “no” vote helped doom his hope of repealing the nation’s health care law. Mr. Trump was not invited to McCain’s funeral.

Nancy Cordes contributed to this report.