The Democratic presidential debate Sunday night could be the liveliest one yet.

In their final debate before voting begins on Feb. 1, Hillary Clinton will be more aggressive in her attacks on Bernie Sanders after the former secretary of state watched her hefty lead in early nominating states evaporate.

Sanders, an independent senator from ­Vermont, has slowed Clinton’s momentum and scored some key endorsements. Former Maryland Gov. Martin O’Malley will be there, too.

What to watch for:

Guns: This will be the first debate since ­President Obama announced his executive actions on guns, creating a new opening for Clinton to slam Sanders again on the issue.

She has lambasted Sanders for voting to shield gun manufacturers from lawsuits.

Both have said they support Obama’s actions expanding the number of background checks before gun purchases by requiring more ­sellers — including those at stores, gun shows and on the Internet — to get licenses.

Strategy: Clinton had a standout performance at the first debate but stumbled in the second and third by invoking the Sept. 11, 2001, terrorist attacks to explain her relationship with Wall Street. She also said that the U.S. is “finally where we need to be” in the fight against the Islamic State in Iraq and the Levant.

Aides said that Clinton needs to show she is above the fray by not getting flustered by tough questions or attacks on her record.

Sanders’ status as a genuine threat to Clinton also puts pressure on him to withstand attacks and demonstrate a command of issues.

Race relations: Clinton has a big lead over Sanders with black voters in South Carolina, the debate site, where the primary election will be held Feb. 20. More than half the primary voters in South Carolina in 2008 were black.

Health care costs: Clinton has stepped up criticism of Sanders for failing to say how he would pay for a health care plan that some have estimated to cost $15 trillion.

Clinton has said it’s impossible to implement Sanders’ plan without raising taxes. She has pledged not to raise taxes on the middle class.