Myrtle Beach, South Carolina —

“South Carolina is Graham Country.”

So read the signs at the Myrtle Beach Convention Center, where President Donald Trump rallied on Friday for the sister of his late friend, Sen. Lindsey Graham.

Tuesday’s Republican runoff — between appointed Sen. Darline Graham and Rep. Ralph Norman — will test the power of Trump’s endorsement after several of his candidates have come up short in recent primaries and ahead of a November midterm election where the GOP is banking on the base to help defend its congressional majorities.

With turnout on the line, Trump understood his assignment, touting Graham as a “very special person” whom he asked to run for her brother’s seat.