By Steve Holland &Emily Stephenson
South Carolina Governor Nikki Haley, viewed as a possible Republican vice-presidential candidate, has endorsed US Senator Marco Rubio for their party's 2016 White House nomination, three days before the state's presidential primary.
"If we elect Marco Rubio, every day will be a great day in America," Haley said with Rubio at her side at an event in Chapin, South Carolina.
Haley's endorsement gave Rubio, 44, a valuable ally to try to sway voters in South Carolina, the third contest after Iowa and New Hampshire to pick a party nominee for the November 8 presidential election to succeed Democratic President Barack Obama.
Rubio is seeking to take second or third place in South Carolina's Republican primary on Saturday and potentially emerge as the main Republican establishment alternative to front-runner Donald Trump, who has a big lead in the state.
The endorsement came as a new wave of bickering broke out between Trump and US Senator Ted Cruz of Texas, who is in second place in the polls in South Carolina.
Trump threatened to sue Cruz over an anti-Trump TV ad that expressed doubts about Trump's statement he is a conservative.
The daughter of Indian immigrants, Haley, 44, seized the spotlight in January when in the Republican response to Obama's State of the Union speech she set herself apart from the party's presidential candidates by calling for tolerance on immigration and civility in politics.
Last year she gained national attention by leading an effort to remove the Confederate battle flag from the state Capitol grounds after the killing of nine black churchgoers in Charleston.
Some political analysts have said she could be picked as the Republican vice-presidential nominee.
Haley's endorsement of Rubio was a blow to the candidacy of former Florida Governor Jeb Bush, coming two days after Bush's brother, former President George W. Bush, met with Haley privately in the state capital, Columbia.
"Disappointed" was Bush's response to the endorsement.
"She's a very good governor and should I win the nomination, there'll be a role for her in the campaign," Bush, 63, told reporters after a campaign event in Summerville, South Carolina.
"Trust me, she's a great person."