WASHINGTON -- U.S. President Donald Trump assured a high-profile gathering of Christian conservatives on Friday that his administration will defend religious organizations, promising a return to traditional American values while again subtly stoking the fire he helped ignite over NFL players kneeling during the national anthem.

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

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.

He bemoaned the use of the phrase "Happy Holidays" as a secular seasonal greeting and vowed to return "Merry Christmas" to the national discourse.

He noted, as Christian conservatives often do, that there are four references to the "creator" in the Declaration of Independence, saying that "religious liberty is enshrined" in the nation's founding documents.

"I pledged that in a Trump administration, our nation's religious heritage would be cherished, protected and defended like you have never seen before," Trump said. "Above all else in America, we don't worship government. We worship God."

Trump praised his repeal of the Johnson Amendment, which limited political activity or endorsements by religious groups that received tax exemptions, as well as his administration's effort to expand the rights of employers to deny women insurance coverage for birth control. The White House has also issued sweeping guidance on religious freedom that critics have said could erode civil rights protections for lesbian, gay, bisexual and transgender people.

Trump waded again into the cultural war that has captured his attention in recent weeks, declaring to loud applause that "we respect our great American flag," a not-too-subtle reference to his repeated denunciations of NFL players who have taken to kneeling during the national anthem.

But Trump also struck several empathetic notes, offering condolences to the victims of Las Vegas mass shooting and pledging support to the people of Texas, Florida and Puerto Rico which have been ravaged by recent hurricanes. His kind words for Puerto Rico stood in stark contrast to his tweets the day before when he declared that federal personnel would not be able to stay "forever" to help the island, which remains largely without power weeks after the storm.

The president also made a call for Congress to enact his agenda, including a tax cut by the end of the year. And he vowed again to undo the Obama health care law, chiding Congress for forgetting "what their pledges were so we're going a little different route." The night before the speech, the administration announced it would halt payments to insurers, a move certain to roil insurance markets.

"Our values will endure. Our nation will thrive. Our citizens will flourish. And our freedom will triumph," Trump said.

Trump has long been an unlikely favourite of religious conservative voters.

A twice-divorced casino owner, Trump boasted about his wealth and sexual exploits on Howard Stern's radio show and posed for Playboy covers with scantily clad women. Just over a year ago, his campaign was dealt a near-fatal blow when a 2005 Access Hollywood video emerged capturing Trump bragging about committing sexual assault.

But evangelicals largely stood by Trump, who has appeared at the Values Voters summit twice before. In 2015, with questions surrounding whether he would appeal to evangelicals over conservative candidates like Texas Sen. Ted Cruz and former Arkansas Gov. Mike Huckabee, Trump held a Bible aloft and declared, "I believe in God. I believe in the Bible. I'm a Christian."'

Trump appeared before the group against last September, a moment in the electoral stretch run usually devoted to wooing undecided voters, to instead focus on his pitch to his religious base. Though he avoided some hot-button social issues like same-sex marriage and abortion, he vowed his support for Israel, an important issue for evangelicals, and said that it was the "dream" of the Islamic State for his opponent Hillary Clinton to be elected president.