President Donald Trump's evolution from twice-divorced casino owner viewed warily by Christian conservatives to evangelical favorite defending religious liberty was on full display on Friday as he promised a return to traditional American values, including restoring "Merry Christmas" to the national discourse.

Mr Trump, the first sitting president to address the Values Voter Summit, ticked off the promises he's fulfilled to evangelical Christians and other conservatives, pledging to turn back the clock in what he described as a nation that has drifted away from its religious roots.

"How times have changed, but you know what, now they are changing back again, just remember that," he told the cheering crowd.

It was a far cry from the sceptical welcome Mr Trump received when he first addressed the group as a neophyte politician in 2015.

With questions swirling then about whether he could appeal to evangelicals over conservative candidates like Ted Cruz and Mike Huckabee, the former Arkansas governor, Mr Trump held a Bible aloft and declared: "I believe in God. I believe in the Bible. I'm a Christian."'