FOR more than three decades, conservative white evangelicals have been a dominant force within the Republican Party, shaping presidential primary contests and turning out to vote for the eventual nominee. This year, though, the relationship is coming undone, as the party — with the votes of a not insignificant number of conservative white evangelicals — is poised to nominate Donald J. Trump.

For a constituency that has made conservative religious values, sexual purity and Bible-driven policy the cornerstone of its politics, Mr. Trump — the twice-divorced, foul-mouthed businessman who praised Planned Parenthood’s health services and nonchalantly gave Caitlyn Jenner permission to use the women’s room in Trump Tower — seems an odd choice.

The religious right faces a reckoning, not just because members of its ranks supported, enabled or acquiesced to Mr. Trump. His success means religious and political leaders must figure out how a religious movement entangled itself in partisan politics and ended up being marginalized by the party it embraced.

The evangelical-Republican alliance, while certainly formidable and enduring, has suffered from growing tensions. Chief among them are inflexible ideological litmus tests on certain issues, such as abortion and gay rights, while internal disagreements over political issues like immigration, as well as core theological concerns, were shrugged off.