The Christian social activist Shane Claiborne has hit out at Jerry Falwell Jr's failure to challenge the 'un-Christian' policies and 'lifestyle' of Donald Trump, and invoked Jesus's words about the religious elite being like a 'brood of vipers'.

The powerful criticisms from Claiborne come after he was threatened with legal action by Falwell following a request to pray with the president of Liberty University on behalf of his progressive 'Lynchburg Revival' conference which took place last weekend in the Tennessee town that is home to the Christian university. The conference was run by 'Red Letter Christians' who are at odds with Falwell and all his works, and heard voices speaking out against guns, racism and Christian support of Trump.

And it was on the latter issue that Claiborne expanded on The Domenick Nati Show when interviewed by co-host and Liberty University student Nathan Flynn.

'When Jerry Falwell spoke of Trump as the dream president he didn't say this is my dream president; he said this is the dream president for evangelical Christians,' Claiborne said. 'And so when he speaks publicly he is not just represented himself – he is obviously representing Liberty University which is why it became concerning for many Liberty students who said "we want our college to be known more for its love of Jesus than for its love for Donald Trump".'

Claiborne added: 'I think many of us who love Jesus are very concerned right now about the public support of Christians leaders who don't challenge the un-Christian policies and I think lifestyle things as well. I am concerned about Donald Trump's affairs but I am just as concerned about his policies that are affecting people who we are called to love.'

On the snub by Falwell, he said: 'To say you are not welcome to pray on campus, the campus that is the biggest Christian college in the country – it is known, Liberty, for its championing of religious freedom and for putting prayer back in the public schools – and to say that we are not welcome to pray on campus was very troubling and I think that people needed to know that...

'Over and over we're getting a response from parents of current Liberty students and alumni and others [who] are really concerned...This isn't just about Liberty or Jerry Falwell – this is about the state of our country right now and Jerry Falwell is just a symptom of that.'

Pressed by the interviewer on whether it was right to expose the Christian leader, Claiborne said: 'One of the things Jesus does most consistently is challenge the chosen, and include the excluded, so his harshest words – like 'brood of vipers' – were reserved for the self-righteous, religious elite that thought they were the moral gatekeepers of society. Those are the folks he called "a brood of vipers".'

He went on: 'At the heart of our faith is this idea of grace, and forgiveness...But here's the other thing: grace has to go with repentance...and this is what's so important right now when it comes to the public witness of Christianity...we see no signs of repentance...And I don't care whether it's Bill Clinton or Donald Trump: we cannot compromise on the call to repentance. And when Donald Trump is asked about, have you asked God for forgiveness, he says essentially, '"That's not my relationship with God – that's not how we roll." [But] we roll with repentance. That's what we believe.'

Claiborne concluded: 'My concern is really that I want people to really know Jesus and I know that one of the biggest obstacles to Jesus is Christians who have a lot to say with their mouths and very little to show of God's love in our lives and it grieves me that much of our public voices of Christianity haven't always represented the words of Jesus in the Sermon on the Mount.'