As Donald Trump barreled toward his next test of strength in the Republican nomination fight, the billionaire confronted two top U.S. companies, a popular pope and virtually anyone else in his way.

It was just another day on the campaign trail for the Republican front-runner.

The real estate mogul's most dramatic move Friday was to call for a boycott of Apple Inc., following the company's refusal to cooperate with a judge’s order to assist law enforcement in unlocking the iPhone of a California suspect in the San Bernardino shooting rampage that killed 14 people in December.

"Boycott Apple until they give up the information," he said at a rally in Pawleys Island, South Carolina. "The phone is owned by the government."

Trump singled out Apple Chief Executive Officer Tim Cook, saying he's "looking to do a big number, probably to show how liberal he is." Trump later tweeted that he'd stop using his iPhone -- and only use a Samsung device -- until Apple cooperates with authorities.

His remarks came on the final full day of campaigning ahead of two key presidential contests that will shape the tone and duration of the Republican and Democratic races. The six remaining Republicans face off Saturday in South Carolina's primary, while Democrats Hillary Clinton and Bernie Sanders will compete three time zones to the west in the Nevada caucuses.

At an earlier stop, Trump suggested that one of the state's top employers could lose jobs if he isn't elected president because, he claimed, no one else will be as good a negotiator with the Chinese.

“Boeing is building massive plants in China,” he said at a rally in Myrtle Beach. “You have a beautiful plant. Be careful because when they cut the value of their currency, in two years after their plants are built, and you find out you’re losing -- not going to happen if Trump is president, that I can tell you -- but be careful."

Boeing Co.'s 787 Dreamliner assembly plant came on line in 2011 in North Charleston and employs about 8,000 people in the region, part of a manufacturing renaissance the state has enjoyed in part because of its mostly non-unionized workforce.

Boeing doesn't build jetliners outside of the U.S., although it unveiled its largest industrial investment in China last year: a new plant to finish work on planes before they are delivered to local carriers. "Boeing is committed to South Carolina, our workforce and the local community. We have invested more than $2 billion in the state since 2009,'' Elizabeth Merida, a company spokeswoman, said in an e-mail.

Trump, who holds a commanding lead in South Carolina polls, also went after Senator Ted Cruz of Texas, his nearest rival, for being "the biggest liar I have ever seen," and took credit for bringing Senator Marco Rubio of Florida into the fight.

“Even Marco Rubio said, ‘He’s a liar,’ and when a politician says another politician is a liar -- I’ve never heard that before -- I felt so good," Trump said.

Cruz, in turn, launched a new attack on Trump, suggesting that he could not be trusted to pick a conservative justice to fill a Supreme Court vacancy, like the one created by the death of Justice Antonin Scalia.

"If a candidate says — and described himself as very pro-choice and supporting partial birth abortion for the first 60 years of his life -- there’s no reason on Earth to think they’d suddenly wake up and start fighting to appoint conservative justices," Cruz told a crowd at the College of Charleston.

He didn't mention Trump's name, but the reference was unmistakable. Cruz's campaign and allies have been hammering Trump in recent weeks for telling NBC in a 1999 interview that he was "very pro-choice" and wouldn't ban partial-birth abortion.

Cruz, who has been emphasizing his credentials as a former Supreme Court litigator, vowed that if elected president, "every justice I put on the Supreme Court will be a principled constitutionalist" with a "proven record."

"If we elect a Democrat we will lose our constitutional rights for a generation," Cruz said. "But here’s the sad truth: electing a Republican if it’s the wrong Republican doesn’t ensure we keep our rights."

Later during the Cruz rally, some in the crowd chanted, "Dump Trump!"

Cruz also picked up the endorsement of Republican U.S. Representative Mark Sanford during a rally at the College of Charleston.

Rubio, the junior senator from Florida, won the endorsement of South Carolina's popular governor, Nikki Haley, on Wednesday and she has been at his side on the campaign trail ever since. That could give him a significant boost as he continues to try to recover from his worse-than-expected fifth-place finish in New Hampshire's primary on Feb. 9.

"We've got a lot of people watching us today and a lot of people want to know what we're going to do tomorrow," Haley told about 500 people gathered Friday for a Rubio event in the state capital of Columbia.  

"We need to nominate someone that can bring us together," said Rubio, who planned to barnstorm the state by airplane Friday, in his closing pitch. "I know that I can better than anyone in this race. I will bring this party and this movement together, so that we can begin the work of growing our movement."

In a statement Friday, Nevada Democratic Party officials sought to discourage Republicans from attempting any gamesmanship around their party’s caucuses. Republicans caucus there Tuesday.

“We believe that registering under false pretenses in order to participate in the Democratic caucuses for purposes of manipulating the presidential nominating process is a felony," Roberta Lange, the state party's leader, said in a statement. “The Nevada State Democratic Party will work with law enforcement to prosecute anyone who falsely registers as a Democrat to caucus tomorrow and subsequently participates in the Republican caucuses on Tuesday.”

The latest campaign chapter arrives with its share of twists—a staple of the 2016 presidential race. Thursday brought a rare criticism of a White House candidate by a pope.

Condemning Trump's hardline immigration agenda, Pope Francis singled out the New York real-estate developer and suggested that he "is not Christian" because of statements he's made about building a wall on the Mexico border. Trump responded by calling the pope's actions "disgraceful."

At a CNN town hall held hours later in Columbia, South Carolina, Trump softened his tone. "I like his personality," he said of the pope. "I like what he represents. And I certainly have respect for the position."

The dispute between the billionaire and pontiff dominated the campaign Thursday, but it wasn't clear it would have staying power, at least in South Carolina. Catholics represented just 13 percent of state's Republican primary electorate in 2012, according to exit polls. Former Florida Governor Jeb Bush, the race's fiercest Trump critic and a Catholic himself, said Friday on MSNBC it was “inappropriate for the Pope to intervene in the height of a primary.” 

On Thursday evening, in another twist, Michael Bloomberg, founder and majority owner of Bloomberg News parent, Bloomberg LP, spoke at a book party and elaborated on why he is considering a third-party bid for the presidency but didn't announce any such candidacy.

“This really has been a race to the extremes,” Bloomberg said of the current field of candidates, according to a transcript of his remarks.

Turning Point

Known for its beaches, boiled peanuts and barbecue, the Palmetto State has a reputation for picking winners on the Republican side. Since 1980, the winner of the state's primary has gone on to become the nominee every time, with one exception. The outlier was in 2012, when a pair of strong debate performances just ahead of the voting lifted Newt Gingrich to a win over eventual nominee Mitt Romney.

South Carolina is also the first test for candidates in a diverse state and in the solidly Republican southern U.S., so its results could be predictive ahead of contests in March when southern states will host a large proportion of the primaries and caucuses. The state's voting could spell trouble for Bush, who once had hoped to win the state but is trailing in the polls. He brought his brother, former President George W. Bush, out to campaign for him in South Carolina on Monday. 

Bush focused Friday on northwest South Carolina, the conservative heart of the state, where his mother, former first lady Barbara Bush, joined him on the trail. At Wade’s Restaurant in Spartanburg, the 90-year-old matriarch posed for pictures and joked that Jeb Bush was “one of my four favorite sons."

"He’s steady, he’s honest, he is modest, he’s kind, he is good," Barbara Bush said. "All of those things."

Bush pitched himself as the most accomplished candidate in the race. He warned the crowd about backing a candidate who wasn’t ready for the job, and criticized Trump for saying George W. Bush was responsible for the Sept. 11, 2001, terrorist attacks.

“Yes, Mr. Trump, he did keep us safe after 9/11. You’re just dead wrong,” Bush said to applause. "My first job as president of the United States will be to rebuild the military, and to talk a little less."

Democrats vote in South Carolina a week later, so the outcome in Nevada will be felt there. Clinton was believed to have the advantage in the western state because of a heavily Hispanic electorate, but a smattering of recent polls shows the race tied. A Clinton loss in Nevada, after a crushing 22-point defeat by Sanders in New Hampshire, would further stoke doubts about her staying power in a general election against a Republican.

Reflecting the urgency of the Nevada situation for Clinton, her top surrogate and husband, former President Bill Clinton, was set to headline his own midday event Friday in Reno, before joining his wife and daughter for an evening event in Las Vegas.

Clinton is in better shape in South Carolina. A Bloomberg Politics poll released Thursday showed the former secretary of state leading Sanders, 53 percent to 31 percent among likely Democratic primary voters, buoyed by a 3-to-1 advantage among African-American voters.

She received a major boost Friday from the endorsement of the state's highest ranking Democratic African-American politician, U.S. Representative Jim Clyburn. Her campaign also released a new ad narrated by legendary black actor Morgan Freeman that tells the story of her lifetime commitment to "breaking barriers."

The Horserace

A Trump win in South Carolina, a state known for dirty politics and late decisions by primary voters, would be a significant boost for his prospects of winning his party's nomination.

A Bloomberg Politics poll of likely Republican voters in South Carolina released Wednesday showed Trump leading the field with support from 36 percent, followed by Cruz at 17 percent, Rubio at 15 percent and Bush at 13 percent.

Retired neurosurgeon Ben Carson, who has found little success in previous contests in Iowa and New Hampshire, was backed by 9 percent. His candidacy is cutting most into Rubio, who is the second-choice candidate for 24 percent of Carson supporters.

Ohio Governor John Kasich was at 7 percent and may be wasting time and resources in a state that tends to favor more conservative candidates. He's also viewed the least favorably of any of the candidates, although more than a quarter don't even know enough about him to have an opinion.

The Bloomberg poll also shows Trump's strongest part of the state is the so-called Pee Dee region, a northeast section that includes the rapidly growing Myrtle Beach metropolitan area. He leads with 47 percent of the support there, well above Cruz and Rubio, both at 13 percent.

A second-place showing in South Carolina for Rubio would do much to anoint him as the establishment Republican favorite to confront Trump and Cruz. It could also go a long way toward extinguishing the flame of the campaign of his one-time mentor, Bush.

—With assistance from Sahil Kapur, Terrence Dopp, Michael C. Bender, Kevin Cirilli, Julie Johnsson and Justin Sink.

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