Clinton will likely face questions about a trove of hacked emails belonging to her campaign chairman, John Podesta, that were leaked by WikiLeaks. She will also likely face renewed questions about the FBI's decision not to charge her with a crime for using a private email server during her tenure at the State Department.
The Trump campaign has been tight-lipped about how the real estate developer has been getting ready for the third debate. But he was notably resistant to mock debates while preparing for the first two debates, and Trump has regularly mocked Clinton for taking time off the campaign trail for debate-prep.
Clinton has been deep in debate preparations since Saturday, huddling with her top aides at a hotel near her home in Chappaqua, NY, before flying to Las Vegas on Tuesday to continue studying. Although Clinton has emerged as the clear electoral college favorite in recent polls of battleground states, she remains tainted in the eyes of many voters by persistent questions about her trustworthiness.
Inside the Clinton campaign, aides believe that this debate is a critical opportunity for the former secretary of state to make a "closing argument" to voters about her vision for the country. Her objective today, they say, is less focused on baiting or driving down Trump's standing with voters, which the campaign believes to be near or at its basement levels.
Trump has been badly damaged by a string of controversies this month. The lewd remarks in the "Access Hollywood" video shook his support among the Republican leadership, and the recent string sexual assault allegations have strengthened scrutiny of his character and temperament.
Trump has denied all the accusations and has at times mocked the physical appearances of many of the accusers. But the controversies have all but eclipsed Trump's anti-establishment message and his promises to clean up Washington if he is elected.
Recent polls show that he is now running behind Clinton in nearly every battleground state, and he has lost support among independent voters in Florida, Ohio, Pennsylvania and Colorado, all key states.
On Monday, Trump's wife, Melania, defended him during several national television interviews. She downplayed his lewd comments as "boys' talk" and scrutinised the timing of the assault allegations, suggesting they are part of a coordinated effort to hurt her husband's election chances.
Amid diminished chances to win the White House, Trump has complained that the election is rigged in Clinton's favour and has insisted that voter fraud is widespread, which is not supported by evidence. Republican and Democratic leaders alike have condemned such rhetoric.
President Obama lashed out at Trump Wednesday, accusing the GOP nominee of "whining before the game is even over" and warning that such rhetoric could pose a threat to American democracy and undermine voters' faith in the nation's institutions.
"I have never seen in my lifetime or in modern political history any presidential candidate trying to discredit the elections and the election process before votes have even taken place," Obama said.
Obama made the remarks Tuesday at the White House, during a joint news conference with Italian Prime Minister Matteo Renzi.
The Clinton campaign has also forcefully condemned Trump's rhetoric on the "rigged" election, and has accused Trump of trying to distract from the string of sexual assault allegations that have rocked his campaign.
"He's trying to distract from the bad story line of his verbal and physical assaults on women," Palmieri told reporters travelling on Clinton's plane to Las Vegas Tuesday. "Because he's losing and he wants to blame somebody else," Palmieri said, "and that's what losers do."
The Trump campaign has invited two surprising guests to today's debate: Malik Obama, the president's estranged half brother, and Pat Smith, whose son died in Benghazi, Libya, during the 2012 attack on an American diplomatic compound. Smith, who blames Clinton for her son's death, also spoke at the Republican National Convention in July.
The Trump campaign was met with shock and outrage last week in St Louis for inviting several women who had accused former president Bill Clinton of sexual improprieties to the debate. The campaign, which had organised a news conference with the women before the debate, had also sought to seat the women in the family box.
The Commission on Presidential Debates ultimately intervened and prevented the arrangement, which would have had the former president shaking hands with his accusers on national television.
The Clintons have long denied the allegations.
The Clinton campaign, meanwhile, announced that Republican business executive Meg Whitman and billionaire entrepreneur Mark Cuban, a long-time Trump antagonist, would be seated in the debate audience as guests of the campaign. The decision signals that Clinton is likely to also make the economy and Trump's stewardship of his own businesses a factor in today's debate.
