Several of the Republican Party’s most generous donors called on the Republican National Committee on Thursday to disavow Donald J. Trump, saying that allegations by multiple women that Mr. Trump had groped or made inappropriate sexual advances toward them threatened to inflict lasting damage on the party’s image. To an elite group of Republican contributors who have donated millions of dollars to the party’s candidates and committees in recent years, the cascade of revelations related to Mr. Trump’s sexual conduct is grounds for the committee to cut ties with the party’s beleaguered standard-bearer, finally and fully. “At some point, you...