Firstly, Carly Fiorina - the former Hewlett-Packard chief executive who fought her way into the event on a wild card - is a fierce combatant, one whom other candidates will likely tackle with some care from here on in.

Secondly, that many of the candidates have decided it is time to take on the poll leader, Donald Trump.

The debate's host, CNN, had shamelessly promoted the debate, the second of the Republican Party's presidential primary race, as though it was a title fight.

The network then shaped the debate in order to encourage what it called "interaction" between the candidates.

In one early exchange a moderator addressed Ms Fiorina, reminding her that Mr Trump had said of her in a recently published interview: "Look at that face! Would anyone vote for that?"

"Women all over the country heard very clearly what Mr Trump said," Ms Fiorina said with restraint, to some of the loudest cheers of the night.

Mr Trump awkwardly rejoined that Ms Fiorina had a "beautiful face and she's a beautiful woman".

This tone marked a few exchanges. Mr Trump declined to apologise for suggesting that Jeb Bush was soft of Mexican immigration because his wife was Mexican born, before adding: "But I do hear she's a lovely woman."

Florida senator Marco Rubio suggested that on his or her first day in office the new president needed to be up to date on foreign policy, an apparent stab at Mr Trump.

Senator Rand Paul of Kentucky dismissed Mr Trump, saying: "There's a sophomoric quality that is entertaining about Mr Trump."

Wisconsin governor Scott Walker said: "We don't need an apprentice in the White House - we have one right now."

After the debate a member of a CNN focus group said: "[Trump] did not impress me as much as he had in the past but Carly was there and she was steadfast … and she's an outsider."

Most of the field is trying to claim outsider status, even those who are demonstrably senior insiders. Senator Rubio claimed he no longer attended many senate sessions as it was not worth it. Senator Paul introduced himself as a doctor. (He was an ophthalmologist.)

Much of the three-hour debate between the 11 candidates focused on undocumented immigration - an area Mr Trump has made central to the debate - and on Middle East turmoil.

On this issue most candidates agreed that the United States' rivals and enemies had been emboldened by alleged weakness on the part of Barack Obama, though beyond that they differed.

On calls to intervene in Syria, Senator Paul said that in some civil wars both antagonists were evil and there was no benefit in intervention.

While most on the stage advocated scrapping the nuclear deal with Iran negotiated by the Obama administration, Ohio governor John Kasich insisted it would make more sense to see if Iran kept to the agreement first.

With a clear eye on the need to win over evangelical viewers, many candidates took a hard line on abortion.

New Jersey governor Chris Christie - suspected by some on the right of being too moderate – accused Democratic frontrunner Hillary Clinton of supporting "the systematic murder of children in the womb to preserve their body parts in a way that maximises their value for sale for profit".

This was a reference to a scandal surrounding Planned Parenthood, the national reproductive health agency that has been accused by conservative opponents in undercover "sting" videos of harvesting foetal tissue for research for profit. Those allegations have not been substantiated, but Ms Fiorina echoed the points.

There were cheers in the audience but shock in some circles on social media when Mr Bush defended his brother, former president George W. Bush, by saying he had kept America safe.

Some tweeted images of the September 11 attacks, which occurred during his presidency, at this point.

And in another exchange that may come back to haunt one of the candidates, Mr Trump drew a direct link between vaccinations and autism, a controversial stance rejected by doctors and scientists.

During ad breaks a pro-immigration lobby group played advertisements quoting Ronald Reagan's farewell speech, in which he described his vision of "a shining city on a hill".

"In my mind it was a tall, proud city built on rocks stronger than oceans … And if there had to be city walls, the walls had doors and the doors were open to anyone with the will and the heart to get here. That's how I saw it, and see it still."