President Donald Trump headlined a Friday rally in South Carolina for Sen. Darline Graham, using the final stretch of her Republican runoff against Rep. Ralph Norman to test the turnout message he plans to carry into November's midterms: a plea for his supporters to show up even when his name is not on the ballot.

Tuesday's runoff was triggered after neither candidate cleared a majority of the primary vote, as South Carolina law requires for nominating contests, and it pits Graham against Norman, a House Freedom Caucus member who represents the state's 5th Congressional District.

CNN reports that Republican turnout will be decisive for Trump's party as it works to hold the House and Senate this November, and that the president is using Tuesday's South Carolina runoff to workshop the argument he will take to voters over the coming months as Republicans face judgment in the midterms. It is a familiar structural challenge in American politics: the party that holds the White House has historically lost ground in midterm elections, a pattern Trump's turnout push is designed to counter.

With turnout on the line, Trump touted Graham as a "very special person" whom he asked to run for her brother's seat, according to CNN. His message to voters carried an unmistakable appeal.

"The problem that we have, is they say that Trump does great when he's on the ballot. But when he's not on the ballot, his people don't come, and they don't vote for senators, congressmen and other Republicans," the president told the Friday rally. "So, what I really want you to do is pretend, please, that I'm on the ballot."

CNN reports that Trump then cycled through a range of talking points in search of one that would stick. Among them was his 90,000-square-foot ballroom — a project the Supreme Court temporarily allowed him to continue building — which CNN noted provides "little benefit to South Carolinians."

His off-the-cuff asides appeared to draw approval from the Republican audience.

"Look, it's a Friday night. We have plenty of time, right?" he asked the crowd. "What the hell do I have to do? Go back, bomb Iran a little bit more?"

CNN reports that Trump largely glossed over the US war with Iran, which he described as "a little detour," as he blamed inflation on Democrats, promised gas prices will soon come down and claimed his economic poll numbers "should be at 100 percent." CNN added that a recent CNN poll found 65 percent of Americans say his policies have worsened economic conditions.

Even Trump's endorsement of Graham appears to be on shaky ground, CNN reports. Trump would not have been in South Carolina on Friday trying to carry her over the finish line had she won enough votes to avoid a Republican runoff outright. CNN also reports the race has "driven divisions among South Carolina Republicans and even some of the president's allies."

"[B]ehind the scenes, Trump's team is keenly aware that a lot is on the line, especially after some of his chosen candidates have failed to win their primaries," CNN reports.

Some voters remain unpersuaded. A Republican voter identified as "Ross" told CNN he still had doubts about Graham, who took the seat of her brother, former Sen. Lindsey Graham, the onetime Senate Judiciary Committee chairman, after his untimely death.

"A lot of people here are free thinkers," Ross said, speaking with CNN reporters. "And they're going to make up their own minds. But I came here to hear what she had to say."

For Trump, the message heading into November was clear as he and his party face strong headwinds: vote as though you are voting for him, even though you are not. The first test of that argument comes Tuesday, when South Carolina Republicans settle their nominee for the Senate seat.

"And remember, they say, again, that Trump gets a lot of votes, but if he's not on the ballot, people don't vote so much. I am on the ballot. We're all on the ballot," Trump told the crowd.