CHAPIN, S.C. — With days remaining until the South Carolina Republican primary, Gov. Nikki Haley faced a decision: to play kingmaker with her endorsement, or to remain neutral.

She chose Marco Rubio.

Haley and Rubio appeared together for the first time Wednesday at a rally here, where they descended from Rubio’s campaign bus after an introduction by former University of South Carolina quarterback Connor Shaw, another Rubio supporter.

In deciding whom to endorse, Haley told the crowd she had sought “somebody with fight.”

“I wanted somebody with passion. I wanted somebody that had conviction to do the right thing. But I wanted somebody humble enough that remembers that you work for all the people," Haley said. "And I wanted somebody that was going to go and show my parents that the best decision they ever made for their children was coming to America."

That Haley settled on Rubio could shape the fluid race in the final days leading up to the first-in-the-South primary. Donald Trump has maintained a commanding lead here, but Rubio, Ted Cruz and Jeb Bush are locked in a tight contest for second place that has seemed to fluctuate daily. 

Now, Haley’s endorsement gives Rubio a valuable advocate at a critical moment.

“We say every day is a great day in South Carolina,” Haley said in Chapin. “If we elect Marco Rubio, every day will be a great day in America.”

Rubio has cultivated his relationship with Haley, but it was not clear until Wednesday whether Haley would endorse at all. And there was reason to doubt she would pick Rubio: In an interview last month, Haley said Rubio “believes in amnesty,” before later walking back her remark; in 2013, Haley said she “always prefers governors” for the presidency.

She made an exception for Rubio. The endorsement came together following an in-person meeting between Rubio and Haley this week; Haley informed the campaign of her decision Tuesday.

Her support had been highly sought after by other candidates. Bush told NBC News on Tuesday that Haley’s endorsement “would be the most powerful, meaningful one in the state.”

After the news Wednesday that Haley would endorse Rubio, not Bush, a spokesperson for Bush said the former Florida governor “looks forward to having Nikki Haley on his team in the general election.”

Still, the announcement likely deals the most direct blow to Bush, who is competing with Rubio for support from moderate Republicans and big donors, and whose campaign has seemed to sag in South Carolina.

Some of Bush’s South Carolina supporters dismissed the effect Haley’s endorsement would have on his standing in the race. 

"I’m sure she will help Marco some — she’s popular,” said Sen. Lindsey Graham, who has endorsed Bush. “But I feel very comfortable that Jeb’s going to do well."

Cruz’s supporters also responded with nonchalance.

“It’s coming late in the race, and I don’t know how many undecided voters there are out there,” said Rep. Jeff Duncan, who has endorsed Cruz. “I don’t know how much it sways people.”

Indeed, the endorsement might be less of a catalyst for Rubio’s South Carolina campaign than a signal of where it was already headed. After an uneven debate performance sent Rubio’s support plummeting in New Hampshire, he has appeared to bounce back in South Carolina. 

“The governor probably didn’t weigh in on this because she didn’t see momentum,” mused Chip Felkel, a South Carolina Republican strategist. “The timing would suggest that he’s got some momentum to separate himself from (John) Kasich and Bush.”

The timing, just days before the primary, also reflects the tumult and uncertainty in the Republican primary thus far. In 2012, with fewer choices, Haley endorsed Mitt Romney a whole five weeks before the South Carolina primary.

Newt Gingrich ultimately bested Romney, but Haley’s endorsement might carry more weight in this election cycle. Her approval rating has soared to 81 percent among South Carolina Republicans, according to a recent Winthrop University poll.

Haley raised her profile the past year in ways intentional and accidental. After a shooting at a historic African-American church in Charleston left nine people dead, Haley supported removing the Confederate flag from state Capitol grounds. She drew attention again earlier this year with her response to the president’s State of the Union address, in which she bashed Trump-esque politics.

Haley’s endorsement means Rubio has racked up three of the most meaningful endorsements from South Carolina Republicans, with Sen. Tim Scott and Rep. Trey Gowdy also among his backers.

But Haley’s marked “a significant, if not the most significant, representation of the kind of momentum that our campaign is experiencing,” said Rubio senior strategist Todd Harris.

“Given that our campaign was written off for dead just eight or nine days ago, I think that we’re going to surprise a lot of people on Saturday,” Harris said.