“You feel for her as a mother,” said Cheryl Brown, 60, who for years before meeting Ms. McBath, kept a Jet Magazine cover featuring Jordan Davis at her Atlanta-area home. The cover read, “Is Your Child Next?,” and it resonated with Ms. Brown because she, too, fears her black son could fall victim to racist violence.

More than anyone else running for Congress, Ms. McBath, the Democratic nominee in a Republican-leaning race, is redefining social justice in politics this year, in large part through her deep personal connection to the Black Lives Matter movement. Yet she is also far from the only candidate this election cycle to explicitly discuss issues of racial injustice and violence against minorities.

Many Democratic candidates across the country, after years of tiptoeing around issues of race out of fear of alienating white voters, are slowly adopting the language of anti-racist activists. It is an attempt to connect more closely with black voters, in particular, whose turnout will be key in several of November’s most hotly contested midterm elections. Republicans have poured money into advertisements that lambaste Democrats on that move, casting their evolution as a sign of a corroding culture that’s too politically correct.

A new advertisement from the National Republican Campaign Committee about who “owns” the Democratic Party, for instance, begins with an image of Colin Kaepernick, the former N.F.L. quarterback who knelt during the national anthem to protest police brutality.

“Prima donna athletes protesting our anthem” the advertisement begins.

It is a clash that is playing out repeatedly in critical races from Maine to Texas. Observers said such explicit appeals to racial politics are a sign of how cultural fights and political ones have fused in contemporary politics, especially in the era of President Trump and several high-profile police killings of young black people such as Botham Jean in Dallas, who was killed in his own apartment in September.