The second US presidential debate of 2016 went down many rough roads: from Donald Trump's comments in 2005 about grabbing women to Hillary Clinton's 33,000 deleted emails, to Obamacare and Syria, to ISIS and taxes, and even Abraham Lincoln.

In a Sunday night debate filled with tension, Trump accused Clinton of attacking women involved in her husband's marital affairs and declared she would "be in jail" if he were president.

Staring icily at her Republican rival, Clinton said Trump's own aggressively vulgar comments about women had revealed "exactly who he is".

A China reference came shortly after 10:30 pm ET when Clinton said: "China is illegally dumping steel in the United States, and Trump is buying it to build his buildings."

The debate was the culmination of a stunning stretch in the race for the White House, which began with the release of a new video in which Trump is heard bragging about how his fame allowed him to "do anything" to women. A flood of Republicans revoked their support, with some calling for him to drop out of the race.

Answering for his words for the first time, Trump denied that he had ever kissed and grabbed women without their consent. He said repeatedly that his words in 2005 were merely "locker room talk" and paled in comparison to what he called Bill Clinton's abuse of women.

"She should be ashamed of herself," Trump declared. Ahead of the debate, the businessman met with three women who accused the former president of sexual harassment and even rape, then invited them to sit in the debate hall.

Bill Clinton never faced any criminal charges in relation to the allegations, and a lawsuit over an alleged rape was dismissed. He did settle a lawsuit with one of the women who claimed harassment.

"I think it's clear to anyone who heard him that it represents exactly who he is," Hillary Clinton said, adding that she did not believe Trump had the "fitness to serve" as commander in chief.

The second debate was a town hall format, with several undecided voters sitting on stage with the candidates. The voters, all from the St. Louis area, were selected by Gallup.

Clinton said it was OK to have a public and private position on an issue because Lincoln did.

She was responding to a question about an email released by WikiLeaks last week in which Clinton said it's acceptable for a president to project differing positions. She was asked whether that's "two-faced".

She said Lincoln did whatever he could to get the 13th Amendment passed, allowing emancipation of the slaves, by lawmakers who did not support African-American equality.

Clinton said: "I was making the point it is hard sometimes to get the Congress to do what you want them to do. That was a great display of presidential leadership."

Trump began his response to Clinton's statement by rolling his eyes and saying:

"Now she's blaming the late, great Abraham Lincoln."

Trump said a US Army captain killed in Iraq in 2004 would still be alive if he had been president at the time.

Trump was talking about Captain Humayun Khan, whose Pakistan-born father gave an impassioned speech at the Democratic National Convention in July. Trump then got into a feud with Khan's parents.

Trump said Captain Khan is an "American hero" and "he would be alive today if I had been president".

Trump said the United States is allowing refugees from Syria and the Middle East to pour into America and "we have no idea who they are" or where exactly they are coming from.

Asked about bans and strict limits on Muslim immigrants into the United States that he's supported in the past, Trump says it was a policy plan that would grow out of "extreme vetting" of people coming to the US from global conflict areas.

Trump called allowing immigrants into the country without more scrutiny the "Greatest Trojan Horse of all time" and said it had to stop because "we have enough problems in our country".

Clinton said she'll screen Syrian refugees but the country needs to take in more.

Clinton said a proposal like Trump's to ban all Muslims from entering the country plays into the hands of terrorists. She also said Trump has alienated the country's Muslim allies.

Clinton said "we will have vetting and it will be as tough as it needs to be".

Trump said American Muslims must report other Muslims who are engaging in dangerous behavior.

Clinton condemned "dark and divisive" things said about Muslims. She says the United States is not at war with Islam and says Muslims should feel welcome and included in society.

Clinton vowed to fix the Affordable Care Act and Trump is promising to repeal and replace "Obamacare."

Clinton said 20 million more people have health coverage because of the law. She says she wants to "save what works," but the next administration will need to get costs down and provide more help to small businesses. She says if the system is repealed it will be "turned back" to the insurance industry.

Trump says the system is a "disaster" and "will never work." He says it needs to be replaced with a less expensive system that's more flexible for patients regardless of what state they live in.

Trump seems sensitive to his interactions with Clinton. When the moderators asked a question and it was unclear whose turn it was to answer first, Clinton said, "Go ahead, Donald."

Trump replied, "No, I'm a gentleman, Hillary, go ahead."

Clinton and Trump clashed over her use of a private email server while she was secretary of state.

Clinton said she was "very sorry" for using the server, but she takes keeping classified information secret very seriously. She adds there's been no evidence her actions led to classified materials winding up in the wrong hands.

Trump is accusing Clinton of lying, and says she improperly destroyed more than 30,000 emails that he says should have been turned over to law enforcement authorities. Trump says he was disappointed that Clinton had not been criminally charged.

Trump continually tried to pivot to foreign policy, seemingly suggesting his comments pale in comparison to the actions of the Islamic State.