David Jackson

USA TODAY

WASHINGTON — Third presidential debates tend to be the least exciting, but Wednesday's final clash between Donald Trump and Hillary Clinton figures to be an exception.

Trump comes roaring into the prime-time face-off at the University of Nevada, Las Vegas, claiming that the Clinton campaign, the media and the political establishment are conspiring to "rig" the election against him, using "false" stories from women who have accused him of sexual aggression.

"The media is trying to rig the election by giving credence, and this is so true, by giving credence to false stories that have no validity and making the front page," Trump said Monday in Green Bay, Wis.

Will the candidate echo his conspiracy claims in Vegas?

"Trump's participation ensures there shouldn't be many dull moments on Wednesday night," said Aaron Kall, director of debate at the University of Michigan.

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The Democratic presidential nominee has been more low-key heading into the Las Vegas debate, preparing from her home base in New York as her staff deals with a steady stream of embarrassing disclosures from the group WikiLeaks, which has been releasing hacked emails from Clinton campaign officials.

With Trump expected to attack Clinton, and vice versa, this confrontation figures to be a contrast to third debates of the past.

Four years ago, President Obama and Republican challenger Mitt Romney largely held their fire in their last debate. So did Obama and GOP nominee John McCain four years before that.

Presidential nominees are often more cautious the third time around, unwilling to risk an election-changing gaffe or mistake. Most of the campaign issues have been thrashed out by the time third debates roll around, and television ratings tend to drop.

"Generally, it's a bit of an anti-climax," said Alan Schroeder, author of Presidential Debates: Risky Business on the Campaign Trail .

Things seem a lot livelier this time around.

Since the second debate on Oct. 9 — one in which Trump denied ever grabbing women in the manner discussed in a 2005 recording — more than a dozen women came forward to accuse the New York businessman of unwanted sexual advances.

Since then, in rally after rally, Trump has responded to the accusations with election rigging allegations of his own, and more. He has described accusers as liars and criticized their looks. He proposed a drug test before the Las Vegas debate, saying Clinton appeared too "pumped up" during the St. Louis event. The Republican candidate has applauded his supporters' anti-Clinton chants of "lock her up!"

Trump maintained his attacks on Clinton (and the media) while campaigning in Colorado Springs on Tuesday. "Hillary Clinton is the most corrupt person ever to run for the presidency," the GOP nominee told supporters.

He later added: “The press has created a rigged system and poisoned the mind of so many of our voters.”

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Schroeder said Trump "just seems to be giving in to impulse at this point," and may well continue his attacks in this debate. How successful a strategy that would be is open to question, Schroeder said: "He really seemed to be playing only to his supporters and not paying much attention to the big picture at all."

When he hits the stage at UNLV, Trump probably shouldn't engage in his manic behavior of late, said Jo-Renee Formicola, a political science professor at Seton Hall University in New Jersey. Instead, the GOP nominee should act more presidential and "absolutely needs discipline in this debate,” she said.

Chris Wallace of Fox News will moderate the debate that starts at 9 p.m. ET. Among the scheduled topics: debt and entitlements, immigration, economy, Supreme Court, "foreign hot spots" and "fitness to be president."

Clinton, meanwhile, is fighting off allegations associated with emails released by Wikileaks, including dealings between the campaign and Clinton Foundation donors. Trump and allies say the media are ignoring evidence of "pay-to-play" arrangements within Clinton's State Department and the Democratic nominee's tendency to say one thing in public and another in private.

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Headed into this final debate, Kall noted that the second event last week was town-hall-style and included questions from voters that affected the style and rhetoric of the candidates.

"Trump still faced some venue and audience constraints during the St. Louis debate," Kall said. "The public and Clinton campaign are waiting with bated breath to see what an unchained Trump can accomplish during 90 minutes on the debate stage."