COLUMBIA, S.C.  — One of President Donald Trump's earliest and most loyal supporters won a key runoff Tuesday, as South Carolina Gov. Henry McMaster fended off a challenge from a self-made millionaire to secure the Republican gubernatorial nomination.

  • Named governor after departure of Nikki Haley
  • President Donald Trump visited South Carolina to campaign for McMaster
  • In November he'll face Rep. James Smith

The vote tested the heft of Trump's endorsement in South Carolina, where McMaster, 71, was elevated to the governorship he'd long sought early last year following the departure of Nikki Haley to serve as U.N. ambassador. As lieutenant governor, McMaster was the nation's first statewide elected official to back Trump, ahead of South Carolina's early presidential primary.

McMaster — a former state attorney general and U.S. attorney who was elected lieutenant governor in 2014 — has had the last year and a half to develop the mantle of an incumbent. He's tallied up economic development announcements and championed issues aligned with the president's priorities, such as clamping down on sanctuary cities and restricting funding for groups affiliated with abortions.

In November's general election, he'll seek a full term for the office that eluded him in 2010, when he lost a four-way primary to Haley in his first bid for governor.

Tuesday's runoff threatened to embarrass the White House if the governor fell short to businessman and first-time candidate John Warren. Warren largely self-funded his effort and argued he was more similar to Trump than McMaster.

Both Trump and Vice President Mike Pence have visited the state in recent days to campaign for McMaster. During a wide-ranging speech at a rally in West Columbia on Monday night, Trump implored Republicans to back McMaster. Trump pointed to his frequent nemesis, the news media, and warned that a loss for McMaster would be portrayed as a defeat for him.

"So please, get your asses out tomorrow and vote," Trump said. He followed up the rally with a sunrise tweet telling voters McMaster "will never let you down."

Trump has a mixed track record when going all-in for candidates. His preferred candidates have recently lost in Alabama and Pennsylvania.

Two weeks ago, McMaster was the top individual vote-getter in the GOP gubernatorial primary but failed to get the majority needed to win it outright.

In November, McMaster faces Democratic state Rep. James Smith, who won his primary outright.