South Carolina Gov. Nikki Haley endorsed Marco Rubio for president on Wednesday night.
Her endorsement gives Rubio the backing of three of the state's most prominent, and popular, elected officials — Rep. Trey Gowdy and Sen. Tim Scott, both beloved figures in South Carolina, previously endorsed him. Haley appeared alongside Rubio at his Chapin, South Carolina, town hall Wednesday night.
Haley's endorsement, first reported by The Charleston Post and Courier, was heavily courted ahead of Saturday's GOP primary in the Palmetto State. It's a particular blow to the more establishment-minded candidates in the race, and Gov. Jeb Bush told reporters on Wednesday that he was "disappointed" he didn't get her backing.
"I'm disappointed, she's a very good governor and should I win the nomination there will be a role for her in the campaign. Trust me, she's a great person," he said.
Haley was rumored to be leaning towards Rubio, but gave no indication of her decision this week — saying only that she would support anyone from Donald Trump.
Coming just three days out from primary day, Haley's backing could offer Rubio a key boost of momentum as he jockeys for support in a still-crowded field in the Palmetto State.
Recent polling still shows him stuck in third place, behind Ted Cruz in second and Donald Trump with a decisive lead. But he's been gaining support over the past week, with a new Monmouth University poll out Wednesday showing him just two points behind Cruz with 17 percent support among likely GOP primary, and his aides have privately expressed cautious optimism that he could overtake Cruz for second if the race breaks his way.
But the Rubio campaign sees the impact of Haley's endorsement as resonating far beyond South Carolina. Her backing helps him burnish his case as a candidate representing the new face of the Republican Party and the only contender who can expand the GOP tent while unifying the party.
On Tuesday, before the endorsement became official, Rubio made that very case, telling reporters over nachos that "she could help a candidate all over the country."
"She also embodies and exemplifies what I want the Republican Party to be known as in the 21st century — vibrant, reform-oriented, optimistic, upwardly mobile," he said.
This article originally appeared on NBCNews.com.