Samaritan's Purse founder Franklin Graham has denied Donald Trump is a habitual liar and urged Americans to support their president in the face of the country's 'very difficult circumstances'.

Interviewed on MSNBC a year after the death of his father Billy, he was pressed on Trump's 8,158 false or misleading claims identified by the Washington Post.

Graham told Craig Melvin: 'I don't think the president is sitting there behind a desk trying to make up lies, I don't believe that for a second.

'Has he misspoken on something? Sure, all of us do that, you do it and I do it. Sometimes we get the facts wrong, and later on we realise we got the facts wrong or we could have said it better, or it was misrepresented. And so I think the president is trying to do the best he can under very difficult circumstances.'

'We need God and as a nation we've turned our back on God,' he said.

Graham called on Americans to back Trump, saying: 'the thing is the American people have elected Donald Trump... we need to work with him and support him'.

While Trump still rates highly among evangelicals, his support among them has dropped by around seven per cent in the last month.

Graham also hit out on Facebook after reports that a Democrat-led committee had recommended removing the words 'So help me God' from the oath taken by witnesses. Fact-checkers Snopes badges the claim as 'unproven'. Graham said: 'To my moderate, reasonable Democratic friends, let your voice be heard before socialism completely takes over the party. Make no mistake, the progressive agenda is a godless one.'