Republican presidential front-runner Donald Trump drew less than one-half as much interest from debating democrats Sunday night, compared with their last on-stage contest in December.

But he was still the only GOP contender who drew any fire by name as Hillary Clinton, Bernie Sanders and Martin O'Malley tussled in Charleston, South Carolina.

Clinton, the presumptive favorite to win the Democratic nomination, left Trump out of her rhetoric. But Sanders and O'Malley launched broadsides as his positions on Islamic terrorism and global warming.

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GLOBAL WARMING WARRIOR: Vermont's Democratic socialist Bernie Sanders took a climate-change shot at Republican presidential front-runner Donald Trump on Sunday during the Democrats' debate in Charleston, South Carolina

'IT'S A HOAX': Trump had claimed in late December that the climate change movement was a 'hoax' and a 'money-making industry'

SOUTHERN DISCOMFORT: The South Carolina debate brought bitter rivals Hillary Clinton and Bernie Sanders within spitting distance of each other, and included Martin O'Malley as a feisty third wheel

'The debate is over. Climate change is real. It is already causing major problems,' Sanders said in the second half of Sunday night's contest. 'And if we do not act boldly and decisively, a bad situation will become worse.'

'It is beyond my comprehension,' he added moments later, 'how we can elect as President of the United States somebody like Trump who believes that climate change is a hoax invented by the Chinese.'

That line brought laughter from a partisan audience gathered downtown at the Gaillard Center.

Trump indeed said during a December 30 rally in Hilton Head, South Carolina that the modern climate change movement is 'a hoax. I mean, it's a money-making industry, okay? It's a hoax, a lot of it.'

He insisted that 'we don't have to destroy our economy' in order to protect the natural environment.

Trump never said during that appearance that China invented the purported hoax, but did point a finger at Beijing for failing to abide by the same rules the United States agreed to follow in a recently inked multinational climate change deal.

'They're buying all of our coal. We can't use coal anymore, essentially. They're buying our coal, and they're using it,' he said.

In 2012 The Donald tweeted – in a moment he later called a 'joke,' that '[t]he concept of global warming was created by and for the Chinese in order to make US manufacturing non-competitive.'

O'Malley, a former Maryland governor, said Sunday night that he objected to Trump's call for a temporary ban on non-citizen Muslims entering the United States until the federal government can determine 'what is going on' in the wake of a deadly Islamist attack in San Bernardino, California.

DRUNK IN LOVE WITH HILLARY: A Clinton supporter advertised her support from Beyonce during a rally outside Sunday night's debate site

He spoke of a 'political front' in the war against the ISIS terror army.

'If Donald Trump wants to start a registry, in our country, of people by faith,' O'Malley boomed, 'he can start with me!'

'And I will sign up as one who is totally opposed to his fascist appeals that wants to vilify American Muslims. That can do more damage to our democracy than anything.'

Sanders had already drawn the billionaire's blood, saying earlier that all three Democrats on stage had 'denounced Trump's attempt to divide this country, the anti-Latino rhetoric, the racist rhetoric, the anti-Muslim rhetoric.'

The focus on Trump to the exclusion of all the other Republicans may indicate that Democrats fear the real estate tycoon more than the establishment candidates who want to unseat him at the top of the GOP pyramid.

ROUNDING UP CATHOLICS? Martin O'Malley (left) said that if Donald Trump (right) wants to segregate Americans by religion – meaning Muslims – 'he can start with me!'

IT'S GO TIME: The lawn of Charleston's Gaillard Center became a forest of yard signs Sunday night

Sanders made a point of emphasizing his poll numbers in a hypothetical head-to-head matchup with The Donald when he made his case that the Democratic Party should nominate him instead of Clinton.

'In terms of polling, we are running ahead of Secretary Clinton in terms of taking on my good friend Donald Trump,' Sanders said.

In the December 19 Democratic debate there were no fewer than nine separate mentions of Trump's name – including a controversial claim from Clinton that her league-leading Republican counterpart 'is becoming ISIS' best recruiter. They are going to people showing videos of Donald Trump insulting Islam and Muslims in order to recruit more radical jihadists.'

That contention was never backed up, although propaganda videos introduced later featured both Trump and Clinton.

O'Malley said that night that the United States 'must never surrender our American values to racists, must never surrender them to the fascist pleas of billionaires with big mouths.'