What Haley's Endorsement May Mean for Rubio

South Carolina Gov. Nikki Haley threw her support behind presidential hopeful Marco Rubio Wednesday, ahead of the state's Republican primary Saturday -- the jewel in the crown of Rubio's Palmetto State endorsements.

Haley's nod could be a big boost for Rubio. But other campaigns are putting their own spin on it, suggesting the endorsement could be a double-edged sword for the Florida senator.

Without a doubt, Haley is popular in South Carolina: Her approval rating is 81 percent among Republican primary voters in the state, according to a Winthrop University Poll conducted in December 2015.

And she's been showering Rubio with praise.

"I wanted 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 Wednesday at a campaign event alongside Rubio in Chapin, South Carolina.

In an interview with Fox News, Rubio acknowledged Haley's reputation in the Palmetto State was a plus.

"She has built up an incredible reputation here in South Carolina and across the country," Rubio said.

And he could use a bounce: According to a new Fox News poll released on Thursday, Rubio sits third place in the state. Donald Trump is holding onto a double digit lead over Texas Sen. Ted Cruz.

But the 2016 presidential campaign has demonstrated that endorsements might not change voters' preferences so much as reinforce them. For example, when Alaska governor Sarah Palin threw her support behind Trump, 81 percent of Republican voters said her endorsement of Trump made no difference in their vote, according to a recent ABC News-Washington Post poll.

Cruz's campaign, which also courted Haley's endorsement, argued that her backing puts the pressure on Rubio.

"Anything short of a first-place finish in South Carolina for Marco Rubio is a loss," argued Jason Miller, a senior adviser for Cruz's campaign, Politico reported.

"He has the very popular sitting governor, very popular junior senator [Sen. Tim Scott], very popular upstate congressman [Rep. Trey Gowdy]. He has every favorable position going for him that he could ever hope to have. If Rubio can't win here, under these favorable circumstances, where can he win?" Miller said, according to Politico.

Despite saying on Tuesday that Haley's endorsement may be the most meaningful in the state and then yesterday expressing disappointment initially at not receiving Haley's support, Jeb Bush tried to minimize its import.

"She endorsed Mitt Romney last time and he came into the state with a big lead and Newt Gingrich won by 20," Bush said in an interview on "The Kelly File" Wednesday. "So it's a volatile time."

Nevertheless, the Florida senator said he is honored to have Haley's support.

"She embodies for me everything that I want the Republican Party and the conservative movement to be about," he said.

ABC's Candace Smith contributed to this report.

Get real-time updates as this story unfolds. To start, just "star" this story in ABC News' phone app. Download ABC News for iPhone here or ABC News for Android here.