This majority has triumphed in securing retrograde positions that include making no exceptions for rape or women’s health in cases of abortion; requiring the Bible to be taught in public high schools; selling coal as a “clean” energy source; demanding a return of federal lands to the states; insisting that legislators use religion as a guide in lawmaking; appointing “family values” judges; barring female soldiers from combat; and rejecting the need for stronger gun controls — despite the mass shootings afflicting the nation every week.

The platform also makes homophobia and the denial of basic civil rights to gays, lesbians and transgender people a centerpiece. It repudiates same-sex marriage, despite strong support for this constitutional right in the nation at large. The party invokes “natural marriage” and states’ rights for determining which bathrooms transgender people may use, and it defends merchants who would deny service to gay customers.

Optimists who show up every four years as members of the Log Cabin Republicans, a gay rights group, had to admit this was “the most anti-L.G.B.T. platform in the party’s 162-year history.”

It is hard to believe the Republicans’ platform came just three years after party leaders, stunned by the drubbing they took in President Obama’s re-election, commissioned what came to be called a G.O.P. autopsy. It candidly admitted that polls showed the party was harmed by a public perception that “the G.O.P. does not care about people.” Young voters “are increasingly rolling their eyes at what the party represents,” the report warned, while “many minorities wrongly think that Republicans do not like them or want them in the country.”

Enter Mr. Trump, and three years later his dangerous nativism has turned that post-2012 warning into a terrible prophecy. Party officials who once spoke of the need for immigration reform have been silenced. The planks of 2016 have been fashioned as underpinnings for Trump jingoism.