Activists and leaders in the social conservative movement, after spending most of the past year opposing and condemning Donald J. Trump, are now moving to embrace his candidacy and are joining the growing number of mainstream Republicans who appear ready to coalesce around the party’s presumptive nominee.

Though their support for Mr. Trump is often qualified, this change of heart is one of the more remarkable turns in an erratic and precedent-defying Republican campaign. It reflects the sense among many Republicans that, flawed as they may see him, the thrice-married billionaire is preferable to the alternative.

“Oh, my, it’s difficult,” said Penny Nance, the president of Concerned Women for America, a group that has openly campaigned against Mr. Trump. “He’s not my first choice. He’s not my second choice,” she added. “But any concerns I have about him pale in contrast to Hillary Clinton.”

And Mr. Trump — whose litany of offenses against cultural conservatives include support of Planned Parenthood, past positions on abortion rights and his more accepting views on gays and lesbians — is winning over this once deeply skeptical constituency.