Clinton, Sanders set to clash in pre-Iowa debate

Washington - With the Democratic presidential nomination at stake, frontrunner Hillary Clinton squares off in a debate Sunday against Bernie Sanders, whose campaign could be hitting its stride two weeks before the first nomination vote in Iowa.

The pair, along with Maryland former governor Martin O'Malley, take the stage in Charleston, South Carolina with the temperature rising in the primary battle.

All three are aware that their performance - the final Democratic debate before the Iowa caucuses on February 1 - could have a crucial impact on who wins the state.

Establishment Democrats are wary of a repeat of 2008, when Clinton led all rivals into the Iowa home stretch, only to lose the state to little-known senator Barack Obama, who pulled the rug out from under his rival and eventually won the nomination and the White House.

Clinton is the presumptive favourite again. But last year's scandal about her use of a private email account and private server while secretary of state has lingered, and her favorability ratings are lower than those of Sanders.

O'Malley, despite stage time with the other candidates, has made no substantial headway in polls and is seen by many as an also-ran.

While leading nationally, Clinton suddenly finds herself under threat of losing the first two state contests, in February 1 in Iowa, where the pair are neck and neck in the polls, and February 9 in New Hampshire, where Sanders has a significant lead.

All too aware of the Sanders surge, Clinton sharpened her offensive against him this past week, highlighting their policy differences with the self-declared democratic socialist on guns, health care and taxes.

Charlotte was the scene last year of a horrific murder of nine African-Americans gunned down in a church, and gun control is likely to feature prominently at the debate.

Clinton has assailed Sanders for being weak on gun control. This past week she released ad knocking Sanders on firearms and his votes against a landmark bill requiring background checks for gun sales.

"It is time to pick a side," Clinton says in the spot. "Either we stand with the gun lobby or we join the president and stand up to them."

Sanders, for his part, has accused the former first lady of having cozied up to billionaires and said she would not be tough enough on Wall Street banks. He will mine that vein further on Sunday.

America's battle against Islamic State extremists is also expected to be on the agenda.

One sticking point is the peculiarity of the Democratic debate schedule.

The Democratic National Committee (DNC) scheduled its first debate on a Tuesday in October - the Republicans began debating in August.

Since then the Democrats have held weekend affairs only, including the latest during the Christmas shopping rush on a day that, stunningly, coincided with the opening day of the much-awaited new Star Wars movie.

Republicans seized on the schedule to accuse Democratic leadership of seeking to protect Clinton from excessive on-stage criticism that would be seen by millions.

The DNC "could be doing a much better job of showcasing its candidates," the Las Vegas Review Journal wrote in a recent editorial.

"Nowhere is this more evident than in the DNC's curiously weak debate schedule." Last Thursday's Republican debate was engaging, rowdy, bizarre, and tense.

All six Republican showdowns have been must-see TV for political junkies and for Republican voters eager to not only study the difference between the several candidates, but to wonder at the bombast of frontrunner Donald Trump.