Lindsey Graham has repeated his call for Joe Biden to be impeached over the US withdrawal from Afghanistan, saying the president “ignored sound advice” and has “been this way for 40 years”.

Some observers may harbour doubts about Graham’s sincerity.

The Republican senator from South Carolina was close to Biden when Biden was a senator, a relationship which remained strong when the man from Delaware became vice-president to Barack Obama.

Only six years ago, in 2015, Graham told the Huffington Post: “If you can’t admire Joe Biden as a person, then you got a problem. You need to do some self-evaluation. ’Cause what’s not to like?”

Furthermore, Graham reportedly called Biden in mid-November, seeking to explain both his enthusiastic support for Donald Trump’s refusal to admit defeat and his championing of attacks on Hunter Biden, the president’s only surviving son, during the election campaign.

Biden rebuffed him, the New York Times reported, the call proving “short, and not especially sweet”.

On Sunday, amid a cacophony of comment and invective over Afghanistan from Biden’s advisers and opponents, Graham gave a short interview to CBS’s Face the Nation.

Calling for US forces to remain in the country, to tackle terrorists who killed 13 US troops and as many as 170 Afghans this week, he said: “You cannot break [Islamic State’s] will through drone attacks. You’ve got to have people on the ground hitting these people day in and day out. You can’t do it over the horizon.

“[Biden] deserves a lot of accountability for this. And I’m sure it will be coming.”

Graham is not the only Republican to call for Biden to resign or be impeached but as Democrats hold both houses of Congress the idea is a total non-starter. Attacks on Biden are more focused on seeking to inflict lasting damage before midterm elections next year.

Regardless, Graham told CBS he still thinks Congress should make Biden the fourth president it has tried to remove, after Andrew Johnson, Bill Clinton and Trump.

“I think it’s dereliction of duty to leave hundreds of Americans behind enemy lines, turn them into hostages, to abandon thousands of Afghans who fought honourably along our side, to create conditions for another 9/11 that are now through the roof,” said Graham.

As a senator, Graham was a juror in Trump’s two impeachment trials. He voted against convicting him for seeking dirt on Biden in Ukraine and inciting the deadly Capitol riot.

“Yeah, I think [Biden’s] been derelict in his duties as commander-in-chief,” Graham told CBS. “I don’t think he got bad advice and took it. I think he ignored sound advice.

“And this is Joe Biden being Joe Biden. He’s been this way for 40 years, but now he’s the commander-in-chief. He’s not a senator. He’s not the vice-president. These are commander-in-chief decisions. I think the best you could describe is dereliction of duty at the highest level.”

Rather than challenge Graham about his many changes of heart about Biden, host Ed O’Keefe ended the interview by calling the senator “an erstwhile friend of the president” who “obviously disagrees with him on this”.

After Graham’s call to Biden was reported, Biden told Stephen Colbert: “Lindsey’s been a personal disappointment, because I was a personal friend of his.”