Senator Tim Scott of South Carolina is President Trump’s highest-profile Black supporter, but he didn’t use his convention speech to make a stalwart defense of Mr. Trump’s first term.

Instead, Mr. Scott, the first Black person to serve in both the House and Senate, offered his own life story, from growing up sharing a bedroom with his mother and brother in his grandparents’ home to first getting elected to Congress in 2010.

And while the rest of the speakers on the first night of Mr. Trump’s convention painted the picture of an apocalyptic nation needing to be rescued by its incumbent president, Mr. Scott offered a far more optimistic vision of America — one where his rise “from cotton to Congress in one lifetime” is possible.

“Our nation’s arc always bends back toward fairness. We are not fully where we want to be, but I thank God almighty we are not where we used to be,” Mr. Scott said. “We are always striving to be better. When we stumble, and we will, we pick ourselves back up and try again. We don’t give into cancel-culture, or the radical — and factually baseless — belief that things are worse today than in the 1860s or the 1960s.”

It is not the first time Mr. Trump has employed Mr. Scott to defend his stewardship in the White House. Earlier this year Mr. Scott defended Mr. Trump’s handling of the nationwide street protests sparked by the police killing of George Floyd in Minnesota.

And at the same time, Mr. Scott said former Vice President Joseph R. Biden Jr., who won the Democratic presidential nomination largely on the strength of his support from Black voters, is both out of touch with Black America and takes its support for granted.

“Joe Biden said if a Black man didn’t vote for him, he wasn’t truly Black,” Mr. Scott said. “Joe Biden said Black people are a monolithic community. It was Joe Biden who said poor kids can be just as smart as white kids.”

Mr. Scott also condemned Mr. Biden for writing the 1994 crime bill “that put millions of Black Americans behind bars.” That political attack is notable given that much of the rest of the evening was devoted to Mr. Trump’s call to be more aggressive with protesters, many of whom are Black.

And, like so many other Republican convention speakers, Mr. Scott said Mr. Trump alone was holding back the Democrats from permanently altering the American character.

“Make no mistake: Joe Biden and Kamala Harris want a cultural revolution. A fundamentally different America,” Mr. Scott said. “If we let them, they will turn our country into a socialist utopia, and history has taught us that path only leads to pain and misery, especially for hard-working people hoping to rise.”