News Analysis: Trump's challenge in final debate: hit Clinton hard while looking presidential

Controversial Republican candidate Donald Trump will face a tough challenge for the third and final U.S. presidential debate on Wednesday - hit rival Hillary Clinton hard on her alleged corruption, while looking like a president.

The debate comes as the clock winds down toward Election Day on Nov. 8, and also comes amid new allegations of corruption on the part of Clinton. But capitalizing on this in a way that benefits Trump's campaign may not be easy for the brash billionaire.

Trump has certainly had times in which he appeared "presidential," such as when he delivered serious policy speeches on U.S. national security and the economy in recent months. But those were pre-written addresses, and the New York mogul stuck to the script while reading them. In sharp contrast, Trump often and easily gets himself into trouble when speaking off-the-cuff. He often makes insulting remarks that turn off moderate voters who are looking for a candidate they could picture in the White House.

Indeed, U.S. voters usually cast their ballots based on their perception of a candidate, and therein lies Trump's problem. While his die-hard supporters love what they see as a candidate who is thumbing his nose at the Washington establishment, more moderate voters and independents see a candidate who is obnoxious and seems more like an entertainer than a president.

Trump cannot win solely on the votes of his core supporters, and the GOP nominee needs to broaden his appeal as the clock ticks toward Election Day, experts said.

"Trump's biggest obstacle is passing the threshold of acceptability as president," Brookings Institution Senior Fellow Darrell West told Xinhua.

Trump needs to reassure people that he is up to the job, knows enough to make smart decisions, and has the proper temperament to be president, West said.

"Public opinion surveys show that over 60 percent of voters think he is unfit to be president. He has to address that concern by showing that he understands the job and is capable of handling it," West said of how Trump should handle himself in Wednesday's debate.

Dan Mahaffee, an analyst with the Center for the Study of the Presidency and Congress, told Xinhua that while Trump did well during the previous debate, he was unable to appeal to moderate voters.

"Moderates-both Republicans and independents-have been turned off by his temperament and policy approach," Mahaffee said.

"Furthermore, the steady stream of accusers describing sexual assault by Trump has continued to keep that story in the headlines... (and has) continued to solidify the anti-Trump vote among moderates and Hillary supporters," Mahaffee said, referring to recent allegations by several women who claimed Trump sexually harassed them. Trump denies the accusations.

Trump will continue to push to build momentum among his populist base, but his approach largely suggests that his strategy may be to drag Clinton's support down rather than expanding his coalition.

"This approach has its limits, as it has combined with his other scandals to limit his support among key swing constituencies, and now we see traditionally Republican states like Utah, Arizona, and Georgia becoming competitive even though nationwide polls may appear close," Mahaffee said.

If Trump has indeed limited his outreach to moderates, this debate is important for both parties to fire up their respective bases, although Clinton may try to find a balance between firing up her base and broadening her coalition to bring in more moderate voters who are turned off by Trump, Mahaffee said.

Julian Zelizer, professor of history and public affairs at Princeton University, told Xinhua that in the last debate Trump managed to energize his base and it looks like, for the time being, prevent any serious damage to his candidacy.

"But he did nothing to expand his support and, combined with allegations, he has seen his support diminish in battleground states," he said.

Zelizer added that Wednesday's debate is very important. "These debates have taken on added significance just given how unpredictable they are and how many people are watching each one," he said.

Despite controversies over his sexist comments - caught on tape from several years ago - and alleged sexual harassment, new information about Clinton may give Trump some ammunition in Wednesday night's debate.

The website WikiLeaks released hacked emails in which Clinton campaign chairman John Podesta insulted Catholics and suggested that some of the religion's most closely-held beliefs be changed by the state.

The statements sparked an uproar from Catholic leaders, Catholic rights groups and conservative media. The website also released evidence earlier this week that one of Clinton's top aides at the state department tried to make an unethical deal with the Federal Bureau of Investigation. Endit