One of Donald Trump’s most influential conservative Christian backers pulled his endorsement of the Republican nominee on Sunday, even as other prominent Christian supporters stood by him following the release of a video that showed Mr. Trump making lewd comments about groping women.

Just hours before the second presidential debate on Sunday, Wayne Grudem, an evangelical theologian, posted an essay online that declared, “There is no morally good presidential candidate in this election.”

“I previously called Donald Trump a “good candidate with flaws” and a “flawed candidate” but I now regret that I did not more strongly condemn his moral character,” Mr. Grudem wrote. “I cannot commend Trump’s moral character, and I strongly urge him to withdraw from the election.”

The essay was a stark reversal, just a few months after Mr. Grudem, a conservative theologian at Phoenix Seminary in Arizona, made a full-throated endorsement of Mr. Trump, who he deemed a “morally good choice.”

That essay—which ignited debate among evangelicals about whether they could vote for Mr. Trump in good conscience—has now been removed from the website Townhall and replaced with Mr. Grudem’s denunciation of Mr. Trump.