When Jen Hatmaker speaks to stadiums full of Christian women, she regales them with stories about her five children and her garden back in Austin, Tex. — and stays away from politics. But recently she took to Facebook and Instagram to blast Donald J. Trump as a “national disgrace,” and remind her legions of followers that there are other names on the ballot in November.

“Trump has consistently normalized violence, sexual deviance, bigotry and hate speech,” she said in an email interview. “I wouldn’t accept this from my seventh-grade son, much less from a potential leader of the free world.”

In the nearly four decades since Jerry Falwell Sr. founded a group called the Moral Majority, evangelical Christians have been the Republican Party’s most unified and reliable voting bloc in November presidential elections. The leaders of what came to be known as the religious right were kingmakers and household names, like Pat Robertson, James C. Dobson, Ralph Reed.

But this year, Ms. Hatmaker’s outraged post was one small sign of the splintering of the evangelical bloc and a possible portent of the changes ahead. While most of the religious right’s aging old guard has chosen to stand by Mr. Trump, its judgment and authority are being challenged by an increasingly assertive crop of younger leaders, minorities and women such as Ms. Hatmaker.