O’Rourke has endorsed Biden, whom he described as “empathetic and caring” and someone who can “reassert our moral standing in the world at a moment that it’s been called into question.”

CNN reporter Eric Bradner said O’Rourke told him his 13-year-old son Ulysses had swayed him. Ulysses had watched a clip of Biden reflecting on the impact of the deaths of his infant daughter and wife in a car crash in 1972, and, from cancer, of his son Beau in 2015.

The clip in question was from a town hall last month in Charleston, South Carolina, where Anthony Thompson, whose wife was killed in a mass shooting at the Emanuel African Methodist Episcopal Church in 2015, recalled how Biden had come to the scene soon after the killings.

Thompson asked Biden how his faith would inform his decision-making as president. The former VP praised Thompson’s forgiveness of the killer and, visibly moved, said that his faith had given him “hope and purpose.”

Biden said: “I kind of know what it’s like to lose family and my heart goes out to you.”

Bradner tweeted: “Beto O’Rourke tells me he decided to endorse Biden after his son Ulysses pushed him to do so over the weekend.

“He’d decided to vote for Biden last week after seeing this clip. He sent it to his wife Amy and said he thought Biden was “the guy for us.'”

In a follow-up tweet, Bradner wrote how O’Rourke had told his son: “I was going to vote for Biden. And he said, ‘Well, you should endorse him.’ And I said, ‘OK, that makes sense.’ He said, ‘If you want this guy to win, you should do everything you can to help him.’” Newsweek has contacted Bradner and O’Rourke for comment.

O’Rourke, who was representative for Texas’s 16th congressional district until 2019, quit the primary race in November 2019.

His endorsement of Biden is the latest the former vice president has got ahead of Super Tuesday, having secured the backing of Minnesota Senator Amy Klobuchar and former mayor of South Bend, Indiana, Pete Buttigieg.

He is now in a good position to become the Democrat nominee after he surged past progressive rival Senator Bernie Sanders of Vermont, according to FiveThirtyEight’s latest forecast.

The Statista graph below shows polling averages in the states ahead of Super Tuesday.