Democratic presidential candidate and former Vice President Joe Biden disembarks a plane, at New Castle Airport, in New Castle, Delaware, Sept. 21, 2020. Photo: Reuters / Mark Makela.

Cindy McCain, the widow of Senator John McCain, became the latest prominent Republican voice to back Democratic presidential nominee Joe Biden in his bid to wrest the White House from President Donald Trump in November.

“My husband John lived by a code: country first,” McCain wrote in a Twitter post on Tuesday. “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

Biden, who forged a long friendship with John McCain despite their ideological differences, had broken the news earlier during a virtual fundraiser, telling supporters that Cindy McCain decided to endorse him after The Atlantic magazine reported that Trump had called US soldiers who died in combat “losers” and “suckers.”

Trump has denied making the comments. The president and McCain had a history of animosity, after Trump disparaged McCain’s military service and years spent as a prisoner of war in Vietnam during the 2016 presidential campaign. Cindy McCain appeared in a video on Biden‘s behalf at the Democratic National Convention in August.

Trump reacted to the news early on Wednesday with more insults, saying he hardly knew Cindy McCain.

“Joe Biden was John McCain’s lapdog,” he wrote. “Never a fan of John. Cindy can have Sleepy Joe!

John McCain, who represented Arizona in the US Senate for more than three decades and was the 2008 Republican presidential nominee, died of brain cancer in 2018. In August, more than 100 former McCain staffers announced their support for Biden. Recent state polls give Biden a lead in Arizona, which voted for Trump in 2016.

Trump held a campaign rally in the battleground state of Pennsylvania on Tuesday, as the death of liberal US Supreme Court Justice Ruth Bader Ginsburg on Friday continued to reshape the presidential contest.

Trump said earlier on Tuesday he would reveal his pick on Saturday in the hopes of scheduling a Senate confirmation vote ahead of the Nov. 3 election, despite fierce criticism from Biden and congressional Democrats. Replacing Ginsburg would cement a 6-3 conservative majority on the high court.

“We’re going to pick an incredible woman,” Trump said at the rally, where he also mocked Biden for wearing a mask at campaign events.

Biden has slammed Trump’s handling of the coronavirus pandemic, which has killed more than 200,000 people in the United States, more than any other country. Trump has claimed his management of the crisis saved lives.

Biden will return to the campaign trail on Wednesday with his first trip as the Democratic nominee to North Carolina, another key state.

A Reuters/Ipsos poll released on Tuesday showed Trump and Biden even in the state that Trump won in 2016.

Voters in about a half-dozen states have already begun casting early in-person ballots, and election experts expect a surge of early and mail-in voting this year as people try to reduce their risk of exposure to the coronavirus.

The pandemic has helped fuel a slew of lawsuits across dozens of states over efforts to ease mail-in voting restrictions in light of the pandemic. On Tuesday, North Carolina election officials agreed to count absentee ballots received up to nine days after Election Day, as long as they were postmarked by Nov. 3.

Courts in several other key states, including Michigan, Wisconsin and Pennsylvania, have also extended absentee ballot deadlines despite Republican opposition.