Evangelical, Catholic and other church leaders in the United States have published a "call to resist" the Republic frontrunner Donald Trump.

In an open letter, the Christian leaders warn that society is facing a moral crisis, and faith itself is at stake. The fundamental integrity of Christian faith is being threatened by current political realities, they say.

In one of the strongest faith-led attacks on Donald Trump so far, they continue: "We are seeing the very worst values of our nation and its history on display with a vulgar message and style. A direct appeal to the racial, religious, and gender bigotry that is always under the surface of American politics is now being brought to painful public light."

They describe him as a "demagogic candidate" with a message that is "a threat to both the values of our faith and the health of our democracy."

Trump directly promotes racial and religious bigotry, they continue. They argue that he disrespects the dignity of women, harms civil public discourse, offends moral decency, and seeks to manipulate religion.

"This is no longer politics as usual, but rather a moral and theological crisis, and thus we are compelled to speak out as faith leaders."

Trump is bringing the nation's worst instincts to the political surface, they say.

"Trump's highly visible and vulgar racial and religious demagoguery presents a danger but also an opportunity – to publicly expose and resist the worst of American values. By confronting a message so contrary to our Christian values, our religious voices can help provide a powerful way to put our true faith and our better American values forward in the midst of national moral confusion and crisis."

The church leaders say they are obeying an obligation during elections "to lift up the moral values of their faith traditions that offer instruction and guidance on issues of public consequence."

Signatories include Jim Wallis, founder of Sojourners; Shane Claiborne, director of Red Letter Christians; Rev Jim Winkler, president and general secretary of the National Council of Churches; Dr Otis Moss III, of Trinity United Church of Christ; Dr Frank Yamada, president of McCormick Theological Seminary; Father Richard Rohr, founder of the Centre for Action and Contemplation and Dr Steve Schneck, director of the Institute for Policy Research and Catholic Studies at the Catholic University of America

In a commentary on the "Call to Resist" posted by Religion News, Dr David Gushee, professor of Christian ethics and director of the Centre for Theology and Public Life at Mercer University, says he helped draft the letter which was written "prayerfully" and called for it to be shared widely.

He explains: "The statement stems from the shared sense of the signers that the Trump phenomenon challenges Christians at a core moral level, such that faithfulness to Jesus Christ is at stake in how American Christians respond to him."

He argues that Donald Trump has gained a following that now puts him on the brink of the Republican nomination by "exploiting the economic stresses and cultural tensions that exist in our rapidly changing society". Trump has risen to power by deliberately inflaming resentment, in particular white, male, working-class, "Christian" resentment, Gushee says.