I continue to believe that Mr. Trump will not be president: U.S. President Barack Obama

With just four days until the state’s crucial primary, Trump became yet again the focus of attacks by challengers to his front-runner status, including his nearest adversary Ted Cruz who blasted the businessman turned reality TV star as a liberal.

He also traded political punches with Marco Rubio and Jeb Bush and laid out attack lines ahead of the crucial primary, the third in the long party nominations races and the first in the US South.

While Trump was busy scrapping with rivals, Democrat Obama joined the fray, offering a scathing assessment of why he thinks the American people will not elect Trump.

“I continue to believe that Mr. Trump will not be president. And the reason is because I have a lot of faith in the American people. And I think they recognize that being president is a serious job,” he told reporters in California.

“It’s not hosting a talk show or a reality show. It’s not promotion. It’s not marketing. It’s hard,” he said on the sidelines of a summit with leaders and representatives.

Trump, 69, reacted with scorn.

“This man has done such a bad job, he has set us back so far,” Trump said in a television interview, adding however that in a way, being singled out — even for reproach — by the sitting US president was “a great compliment.”

Cruz, a first-term senator from Texas, piled on Trump during a rally in Anderson.

Clearly speaking of Trump, Cruz called on Americans not to nominate and elect a Republican who has “defended abortion or partial birth abortion for the first 60 years of his life.”

The controversial billionaire for his part played up his international business acumen at a rally in North Augusta ahead of Saturday’s primary.

– ‘Why aren’t they beating me?’ -Trump leads handily in South Carolina, with a new CNN poll showing him with 38 percent support over arch-conservative Cruz, who has 22 percent.

The 16-point spread is down from the 20-point RealClearPolitics average, suggesting a softening in some support after Saturday’s bruising debate slugfest.

“Why aren’t they beating me?” Trump taunted, to loud cheers.

Even with his commanding lead, he was calling on supporters to crowd the polls.

“Assume that we’re behind, because you’ve gotta go vote,” Trump said.

Cruz highlighted his experience with Constitutional law in dwelling on a Saturday event that hit the political landscape like an earthquake: the death of conservative Supreme Court justice Antonin Scalia.

Cruz has joined other Republican candidates in insisting that no nominee to replace Scalia be confirmed by the Senate until there is a new president next January.

“We are one justice away from losing our fundamental liberties,” he said, underscoring the stakes of the election as conservatives see the appointment of a liberal judge as potentially ending conservative efforts to overturn landmark cases on abortion, health care and immigration.

Bush, riding high a day after his brother and former president George W. Bush hit the campaign trail with Jeb for the first time, caused an earthquake of his own Tuesday.

Seeking to present himself as the candidate most capable of rebuilding the military, Bush visited a gun manufacturer in state capital Columbia, where he spoke to company employees and walked away with his own personally engraved hand gun.

He tweeted a photograph of the firearm afterwards, with a single word of commentary: “America.”

Bush is the consummate establishment candidate, the son and brother of two presidents. But Trump’s ascension has upended the race, and forced Bush into underdog status.

Trump supporter Jennifer Twilley, reflecting on the anger and frustration coursing through the US electorate, said Trump’s status as a magnate and political outsider made him ideal for the job.

“I don’t really want an established politician anymore,” Twilley, an engineer with General Dynamics who was wearing a pink button that read “Hot Chicks for Donald Trump,” told AFP.

She dismissed the concerns about his braggadocio and confrontational rhetoric.

“I don’t care about the drama, I just want him to fix the financial problems,” she said.

More than halfway through his hour-long speech, a protester interrupted Trump but was shouted down by supporters. She was escorted out of the venue with her middle fingers raised in the air.