By John Whitesides
Tightening polls and rising tensions between White House rivals Hillary Clinton and Bernie Sanders could fuel a fiery Democratic debate on Sunday, their last face-to-face encounter until Iowa kicks off the presidential nominating race in two weeks.
The leading Democratic contenders have stepped up their attacks on each other during the past week, battling over guns, healthcare and Wall Street with growing intensity as polls showed Sanders gaining ground on Clinton in key states.
Clinton, Sanders and former Maryland Governor Martin O'Malley, who lags badly in polls, will participate in the 9pm EST (3pm Monday GMT+13) debate, the fourth between the Democratic contenders.
Foreign policy also could play a role in the debate, which follows Saturday's prisoner deal announced by the United States and Iran.
Sanders, a US senator from Vermont, has pulled into a statistical tie with Clinton in recent polls in Iowa, which holds the first contest on February 1 in the race to pick a nominee for the November election. He also leads Clinton in the next state to vote, New Hampshire on February 9, according to polls.
As the race has tightened, Clinton has been on the attack. The former secretary of state and US senator from New York has hammered Sanders for past votes to support immunity from lawsuits for gun manufacturers and criticised his call for a national single-payer healthcare system. She demanded details on how he would pay for it.
Sanders fired back with an ad criticising Democrats who take money from Wall Street, an obvious dig at Clinton, and touted his plan to break up the big banks. An angry Clinton campaign quickly accused Sanders of breaking his pledge not to air negative ads against her.
"We have differences and that's what I'm focusing on now. We're going to have a spirited debate, I expect, tonight in Charleston," Clinton said on ABC's "This Week" on Sunday.