Even in boycotting a debate with his Republican rivals, front-runner Donald Trump managed to upstage the event on Thursday with a typical dramatic flourish.

Instead of attending a seventh debate, the former reality TV star held a competing event across town that he said raised $6 million (£4 million) for US military veterans. In doing so, he cast a shadow over his rivals, who frequently tossed barbs his way.

Trump's gamble that he could leave the battlefield to his rivals for one night appeared to pay off, with just days to go before Iowa holds the first nominating contest of the 2016 election season. No one appeared to emerge as a central challenger to him during the two-hour face-off in Des Moines.

Trump's refusal to participate in the debate out of anger that Fox News anchor Megyn Kelly was a moderator prompted a flurry of last-minute phone calls with Fox News Chairman Roger Ailes that failed to resolve their dispute.

A Fox News statement said Trump requested that Fox contribute $5 million to his charities in exchange for his attendance, which the network turned down.

The debate was the type of event Republicans would routinely have without the flamboyant Trump on stage, and it lacked the electricity that he brings to the party's search for a nominee for the November 8 election.

Without Trump on stage, former Florida Governor Jeb Bush and New Jersey Governor Chris Christie found themselves with more room to make their case to voters seeking a more mainstream candidate.

Both men have an eye on the February 9 first-in-the-nation primary in New Hampshire, which comes on the heels of the Iowa caucuses on Monday and where an establishment Republican like them might have a better chance of standing out.

Senator Ted Cruz from Texas and Senator Marco Rubio from Florida, the two top challengers to Trump in Iowa, engaged in squabbles over immigration and national security and did not appear to threaten Trump's lead. He holds the edge over Cruz in polls of Iowa Republicans.

Trump's rivals mocked his decision to sit out the debate and found ways to criticise him.

"I'm a maniac and everyone on this stage is stupid, fat and ugly, and Ben, you're a terrible surgeon," Cruz told his rivals, including Ben Carson, a retired neurosurgeon, as the debate opened. His next sentence began: "Now that we've gotten the Donald Trump portion out of the way."

Bush, who has been a frequent target of Trump's attacks, turned a question about religious tolerance into an attack on Trump's proposed temporary ban on Muslims entering the United States.

"Donald Trump, for example — I mentioned his name again if anybody was missing him — Mr Trump believed in reaction to people's fears that we should ban all Muslims. Well, that creates an environment that's toxic in our own country," Bush said.

Cruz, after a series of questions, said: "If you ask me one more mean question, I may have to leave the stage."

In a swipe at both Trump and Cruz, Rubio chimed in: "Don't worry, I'm not going to leave the stage no matter what you ask me."

Social media favourite

With his veterans' event drawing live TV news coverage on Fox News competitors CNN and MSNBC, Trump absorbed plenty of media attention.

He clung to his insistence that Fox News had treated him badly. He has complained that Kelly insulted him at a debate in August and that a statement from the network earlier this week had belittled him.

Two other Republican candidates, Rick Santorum and Mike Huckabee, joined Trump on stage after participating in a debate of low-polling candidates.

Not so former Virginia Governor Jim Gilmore.

"I'm not about to go across town tonight to carry the coat for some billionaire," he said at the "undercard" debate.

There was some mystery as to which veterans' groups would receive the money raised at the event, which included $1 million from Trump himself. His campaign did not say which group was getting the funds.

Trump, with just one day's notice on a weeknight, was able to fill to capacity a hall at Drake University that holds 700.

"I didn't want to be here, to be honest, I wanted to be about five minutes away" at the debate, Trump told the crowd. "When you're treated badly, you have to stick up for your rights – whether we like it or not."

Trump dominated social media during the debate, leading the entire Republican pack in Twitter mentions throughout the first half of the debate, according to data from social media analytics firm Zoomph.

Trump was by far the most-searched-for candidate on Google during the first half of the debate, at one point outpacing the second-most-searched-for candidate, Rubio, by nearly four-to-one, according to Google Trends data.

Trump's support in opinion polls, much of it from blue-collar men, has not wavered for months despite him insulting Mexican immigrants and Muslims and clashing with Republican establishment figures like Senator John McCain.