This comes as Republican Trump held a campaign rally in the battleground state of Pennsylvania on Tuesday.
The president’s relationship with McCain soured after he disparaged the former Arizona Senator’s military service and years spent as a prisoner of war in Vietnam during the 2016 presidential campaign.
However, Biden, despite his ideological differences with John McCain, had forged a long friendship with him.
Trump is falling behind Biden in polls and according to recent state polls, Biden leads the president in Arizona, which voted for Trump in 2016.
Cindy McCain, in a Tweeter message on Tuesday, wrote, “My husband John lived by a code: country first,” noting, “We are Republicans, yes, but Americans foremost. There’s only one candidate in this race who stands up for our values as a nation, and that is @JoeBiden.”
My husband John lived by a code: country first. We are Republicans, yes, but Americans foremost. There's only one candidate in this race who stands up for our values as a nation, and that is @JoeBiden.— Cindy McCain (@cindymccain) September 22, 2020
She had also appeared in a video on Biden’s behalf at the Democratic National Convention in August, during which over 100 former McCain staffers announced their support for Biden too.
Biden had broken the news of the endorsement earlier during a virtual fundraiser, telling his supporters that Cindy McCain decided to back him following a report by The Atlantic magazine that Trump had described as “losers” and “suckers” American soldiers who died in combat.
Meanwhile, President Trump held a campaign rally in Moon Township, Pennsylvania on Tuesday evening, during which he took aim at Biden who he will debate next Tuesday.
“I’m just thinking, but I did more in 47 months than he did in 47 years. It’s true. You look at what we have done," Trump said.