Donald J. Trump had already roiled the religious right, casting the Republican Party’s most reliable voting bloc into an abyss of despair, recriminations and uncertainty about the future. Then the 2005 video surfaced of him boasting about his sexual predations and women began coming forward to accuse him of sexual assault.

“The world is getting a glimpse into the dark and rotting core of evangelicalism,” an evangelical with deep roots in the movement told me recently.

The divide — or, more aptly, the crater — between pro-Trump and anti-Trump evangelicals is a window into the future of the Republican Party. White evangelical voters are the heart of the party’s base, the loyal foot soldiers who turn out for the party’s presidential nominee every time. A poll by the Public Religion Research Institute taken in part after the video’s release shows 65 percent of white evangelicals intending to vote for Mr. Trump. That is high enough to be significant, but is relatively low for evangelical voters and the Republican nominee. (For comparison, Mitt Romney, who was viewed with suspicion by many evangelicals because he is Mormon, won the votes of 79 percent of white evangelicals.) Most telling, though, is the significant gender gap: while 72 percent of white evangelical men said they intend to vote for Mr. Trump, only 58 percent of white evangelical women did.

A defection by even 15 percent or 20 percent of Republican evangelicals from lock-step support for the party could be a major contributing factor to a collapse of its national electoral viability. But that is just one measure of the splintering of this devoted voting bloc. The movement is also being subjected to a very public display of division between the pro- and anti-Trump camps and open talk among evangelicals about pro-Trump leaders’ plummeting credibility.