The senator from Utah appeared to be the first Senate Republican to join the demonstrations over the killing of George Floyd, putting himself at odds with the president again.

Senator Mitt Romney of Utah marched with demonstrators toward the White House on Sunday, appearing to be the first Republican senator to join the thousands across the country protesting the death of George Floyd in police custody.

Mr. Romney shared on Twitter a photograph of himself marching among the crowd, with the caption “Black Lives Matter.”Mitt Romney✔@MittRomney

Black Lives Matter.

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Mr. Romney, who marched with a group of Christians, told a Washington Post reporter that he had joined the protest to show that “we need to end violence and brutality, and to make sure that people understand that black lives matter.”

In joining the protest, Mr. Romney again found himself at odds with President Trump, who has pushed for a military response to the unrest, and standing apart from most of his party, as when he became the sole Republican senator to vote to remove Mr. Trump from office.

Republicans have largely been vocal in condemning the police officers who have been charged in connection with Mr. Floyd’s death, but few have publicly joined protesters marching across the county. Last week, Representative Will Hurd of Texas, the lone black Republican in the House, joined a peaceful protest, marching alongside Mr. Floyd’s family.