Republican White House hopeful Ted Cruz won backing from Indiana's governor on Friday ahead of the state's primary, where the Texan is fighting a rearguard battle to damage front-runner Donald Trump's chances of winning the nomination.
The endorsement from conservative Governor Mike Pence could boost Cruz's hopes of winning Indiana on Tuesday, depriving Trump of some of the delegates he needs at the Republican National Convention in July, which will decide the nominee.
"I'm not against anybody, but I will be voting for Ted Cruz in the upcoming Republican primary," Pence said on an Indiana radio show.
"I see Ted Cruz as a principled conservative who's dedicated his career to advocating the Reagan agenda," said Pence, referring to Republican President Ronald Reagan.
Trump, who described himself this week as the party's presumptive nominee, would take a huge stride toward knocking his Republican rivals out of the presidential race if he wins Indiana.
Cruz, a US Senator from Texas, is trailing the New York billionaire in the Midwestern state after losing to him by a wide margin in all five Northeastern states that held nominating contests on Tuesday.
A CBS poll out earlier this week found Trump with about 40 percent of support in Indiana, compared to 35 percent for Cruz. The poll had a margin of error of 6.6 points. Other polls have also shown Trump ahead.
Despite his endorsement of Cruz, Pence also had kind words for Trump. The governor said he had met with all of the Republican presidential candidates and commended Trump for representing Americans' frustration with Washington politicians.
Pence was once considered a possible presidential candidate but his popularity dropped a year ago after he signed a "religious freedom" bill that critics said was discriminatory against gay people, and then softened the law under pressure from rights groups and businesses.
In a bid to slow Trump's momentum, Cruz named former business executive Carly Fiorina on Wednesday as his vice presidential running mate should he win the nomination. Trump described the move as "desperate."
Trump was in California on Friday ahead of its June 7 primary, when the most convention delegates of the Republican nominating cycle will be at stake. He planned to speak to the state Republican convention later in the day.
About 20 people were arrested outside a Trump rally on Thursday near the county fair grounds in Costa Mesa, California. Media reported that protesters smashed the window of a police patrol car and blocked traffic.
Local news showed demonstrators surrounding vehicles, waving Mexican flags and holding signs. At least one demonstrator was shown jumping on top of a police car.
But the head of California's Republican Party downplayed the demonstrations, and said protests were typical for the state's politics.
"If you're a Republican running for president in California and you don't get protested, you're doing something really, really wrong," Jim Brulte, chairman of the California Republican Party, said on an American TV on Friday. "Every president I've campaigned with here in California has been protested."
Protests have become common outside rallies for Trump. His campaign had to cancel a rally in Chicago last month after clashes between his supporters and protesters.
Trump has won a broad following among Republicans in the United States, along with ardent critics, for his stand on illegal immigration. He has accused Mexico of sending drug dealers and rapists across the US border, and promised to end it by building a wall and making Mexico pay for it.
The population of Costa Mesa, where he appeared on Thursday, is about a third Latino.