He did say the campaign’s strategy of directing surrogates like Mr. Newsom and Mr. Landrieu to out-of-the-way rural towns was an effort to increase turnout in counties that often underperform in the state’s elections.
“Those counties rarely get high-level surrogates,” Mr. Middleton said. “These surrogates have spent time there, connecting with people.”
Even as the Biden campaign has studiously avoided making predictions about turnout on Saturday, Mr. Clyburn on Friday set the benchmark for success at between 150,000 to 200,000 votes, with the president receiving 70 to 75 percent of them.
“Seventy percent would be a success to me,” he said in an interview.
In 2016, when Hillary Clinton defeated Senator Bernie Sanders of Vermont, just over 371,000 people voted. In 2020, with no competitive Republican primary but 12 Democrats on the ballot in a race that was still up for grabs, about 537,000 people voted. South Carolina did not hold a primary in 2012, when President Barack Obama sought re-election and no Democrat filed to run against him in the state.
J.A. Moore, a Democratic state representative in South Carolina who was among the first officials in the state to endorse Ms. Harris’s 2020 presidential campaign, said her frequent visits as vice president had served as a “testing ground” to build relationships with parts of the party’s base — Black voters, young people and women — who were critical to Mr. Biden’s winning general-election coalition in 2020.
“She’s been here building real, connected relationships, specifically in the Black community, but also with women and young people as well,” Mr. Moore said. “Just her showing up to places goes a long way.”
Lisa Lerer contributed reporting.