Just when you thought things couldn't get any more interesting in the Campaign 2016, the Republicans take the stage for their 7th debate Thursday night, minus Donald Trump. But not to worry: Stephen Colbert on Thursday hosted an all-Trump debate - in which Trump debated himself.

During the debate, Colbert asked Donald and Trump several questions, to which the answers are pulled from various clips from the past few years. It added that Trump had offered to appear at the debate upon condition Fox News contribute US$5 million (RM20.64 million) to his charities, which it refused to do.

Fox's Trump-less debate had 12.5 million viewers between 9 and 11 p.m., according to Nielsen. CNN and MSNBC both aired portions of Trump's event dedicated to military veterans, and their ratings put together were about a quarter of the viewers Fox attracted.

Thursday's viewership was way down from the 25 million people who watched the first debate in August - that first sparring session was the most-watched nonsports program in cable news history.

Trump was even a presence at an earlier undercard debate featuring four lower-polling candidates - Carly Fiorina, Mike Huckabee, Rick Santorum and Jim Gilmore.

"I did something that was very risky and I think it turned out great, because I'm on the front page of every paper", Trump told supporters in Nashua, New Hampshire.

"The debate topped all TV Thursday night in total viewers including all broadcast shows", Fox News said in a statement.

"He got pummeled", he repeated before turning to his well-worn attack on Cruz's eligibility to run for President.

But their claim seemed to have been undermined when Ted Cruz revealed what Kelly called the front-runner off-camera.

A recent CNN/ORC poll of Republican voters has Trump at 41 percent to 19 percent for Cruz, with more than two-thirds of Republicans saying they believe Trump will be the party's presidential candidate.

"I'm not going to any Donald Trump event over across town on some sort of faux veteran sort of issue", Gilmore said.

The network said its chairman, Roger Ailes, in conversations with Trump, "acknowledged his concerns" about a "satirical observation" that upset Trump. Trump boycotted the event over Fox's use of Megyn Kelly as a moderator.