Hillary Clinton has attacked her main rival Bernie Sanders on gun laws at the Democratic presidential debate.
When asked if the Vermont senator was strong enough on guns, she said "no, not at all" before vowing to go after the makers of guns used in shootings.
Mr Sanders also attacked Mrs Clinton, saying her support for a no-fly zone in Syria would create "serious problems".
His rallies have drawn big crowds and he has challenged Mrs Clinton's frontrunner status in some key states.
A lot of the key exchanges came between these two and the three other candidates on stage in Las Vegas - former Maryland Governor Martin O'Malley, former Virginia Senator Jim Webb and former Rhode Island Senator Lincoln Chafee - struggled to make headway.
Highlights so far:
biggest applause of the night to Mr Sanders when he said the country was "sick" of hearing about Mrs Clinton's email controversy
but the two argued over the merits of capitalism, with the former first lady saying it would be a "grave mistake" for the nation to reject it
when accused of political expediency, Mrs Clinton said: "I'm a progressive who gets things done"
Mr O'Malley defended his record as mayor in Baltimore, where there were riots this year
Vietnam veteran Mr Webb said his military service gave him leadership skills
one of my strengths is I've never had a political scandal, said Mr Chafee
Mrs Clinton said she wants to be judged on her record not her surname
she said whistleblower Edward Snowden "needs to face the music" and return to the US but Mr
Sanders said he did important work educating the nation about government collection of personal data
former first lady said she would stand up to "bully" Russian President Vladimir Putin
One of the sharpest points of difference between the two main candidates came over gun laws.
The hugely divisive issue came back on the agenda after a mass shooting at a college campus in Oregon.
When Mrs Clinton said her rival was not tough enough, she was referring to him voting in 2005 for a measure to give gun manufacturers immunity from lawsuits.
Vice-President Joe Biden, who is still considering a run for the White House, loomed large despite not actually being on stage.
The debate organisers at CNN set aside a lectern just on the off-chance Mr Biden decided to enter the fray at the last minute.
Mrs Clinton - long seen as the presumptive front-runner - has seen her support wane amid questions about her trustworthiness.
She has been criticised for using a private email account when she served as US secretary of state, a move she now calls a mistake.
Fifteen Republicans are vying to be the party's White House nominee in 2016.
Iowa will be the first state to choose its candidate from each party in February, then other states hold primaries in the following weeks and months.
By next summer, each party will have a presidential nominee who will do battle in the race for the White House.
Votes will finally be cast in November 2016.
