Word spread fast that Melania Trump’s speech at the Republican National Convention on Monday bore striking similarities to one delivered by Michelle Obama at the Democratic convention in 2008, and the furor ignited an intense backlash among blacks posting on Twitter.

While many blacks began accusing Ms. Trump of plagiarism, scores of others went a step further by focusing on the wider racial implications involving the two women and their husbands.

On “Black Twitter,” a term used to describe trending topics among black users on the social media site, #FamousMelaniaTrumpQuotes began trending as people satirically attributed famous lines by black leaders and black musical performers to Ms. Trump. Others altered famous photos from prominent black figures to jokingly accuse Ms. Trump of taking credit for those moments as well.

