NEW YORK -- It could be the greatest political show on Earth.
With a tight election on the line, Republican Donald Trump and Democrat Hillary Clinton face off Monday at their first presidential debate, a battle emerging as the most hotly anticipated moment in modern US political history.
An audience rivaling that of the Super Bowl -- perhaps around 100 million Americans -- will be glued to televisions, smartphones and social media when the rivals rip off the gloves at 9 pm ET. The debate marks a rare shared experience for a country deeply divided along political lines and fragmented in the media they consume.
Suspense has been building for weeks, given the huge political stakes of an increasingly competitive election. And Trump's wild card antics, which will test Clinton's fact checking skills, mean no one can predict how the showdown at Hofstra University in New York will unfold.
The stakes of the debate are monumental.
Clinton, the Democratic nominee, is clinging to a narrow lead in many national polls, but now has almost no margin of error in the battleground states that will decide who will take the oath of office as the 45th President in January. A CNN/ORC poll released Monday found Trump edging Clinton 42% to 41% in Colorado among likely voters in a four-way race. In Pennsylvania, the poll found Clinton in a virtual tie against Trump among likely voters at 45% to 44%.
The Democratic nominee's task is to knock Trump off balance and force him to stick to facts instead of the vague -- sometimes outrageous -- statements he made during the GOP primary debate.
Trump, meanwhile, faces the challenge of bringing his unconventional style to one of the most traditional venues of a presidential campaign. His outsider campaign represents a repudiation of US domestic and foreign policy and if the debate helps convince Americans to elect him, he will lead the nation on a sharply different course than the one President Barack Obama has charted for nearly eight years.
The destiny of the Supreme Court is up for grabs and the GOP's control of the Senate is on a knife-edge in an election that has sparked fierce controversies about race, faith, gender and the nature of America itself.
But there's another factor that makes Monday's debate, the first of three scheduled clashes, so significant.
Clinton and Trump happen to be two of the most famous people in the country -- if not the world -- and their triumphs and disasters over the past quarter-century have reverberated far wider than the political bubble, embedding them in the fabric of American life.
National cultural moment
In fact, the glass-ceiling-shattering female icon and the real estate magnate and reality star-turned-unlikely politician have the potential to lift the debate out of the political realm into a national cultural moment. It could be the kind of event where everyone will remember where they were when they saw it unfold.
"We have never seen any kind of interest like this, and probably never will ever again," said Aaron Kall, director of debate at the University of Michigan and editor of a new book called "Debating the Donald."
The 70-year-old Republican nominee has shattered every rule and convention in politics with his stunning presidential campaign, so there is no reason to think he will suddenly moderate his free-wheeling style with the whole world watching.
Clinton, in facing a rival so instinctive and unpredictable as Trump, faces an assignment no previous nominee has confronted in the 56 years since John F. Kennedy and Richard Nixon held the first televised presidential debate.
"It a watershed," said David Cram Helwich, a debate specialist at the University of Minnesota, who has carried out an in-depth study of Trump's debate technique. "Trump is a candidate who has defied all conventions of how one approaches these debates. It's unpredictable since he does not feel bound by traditional presidential debate convention and he could do whatever it is that he wants to."
But Clinton, 68, will make her own history as the first woman leading her ticket into a presidential debate -- a factor that could shift the dynamics of the previously all-male showdown and present her tough-talking rival with his own challenges.
Not even Trump seems to know how he will behave.
"If she treats me with respect, I will treat her with respect," Trump told Fox News' Bill O'Reilly last week. "It really depends. People ask me that question, 'Oh you're going to go out there and do this and that.' I really don't know that. You're going to have to feel it out when you're out there."
Clinton has in the past shown herself adept at capitalizing on any perceived sexism during debates. And Trump's worst moments in the primary season debates came when he was challenged over his Alpha Male approach by powerful women like Carly Fiorina or Fox News anchor Megyn Kelly.
Trump and Clinton enter the showdown with clear goals.
The billionaire real estate developer and neophyte politician must quell doubts that he lacks the knowledge, empathy, and temperament needed to serve in the world's most unforgiving job, the presidency of the United States.
Clinton's policy expertise and experience are not in question. But her character and honesty are. The ex-secretary of state needs to show a glimpse of humanity to connect with Americans in the way she never has before. She particularly needs to woo millennials crucial to her White House hopes.
Clinton, who characteristically has been prepping with briefing books and participating in mock debates with her tart-tongued former aide Philippe Reines playing Trump, must also avoid being thrown on the defensive about ethics.
Trump is likely to bring up her private email server, allegations about the Clinton Foundation and past scandals involving her and former President Bill Clinton to paint her as the corrupt status quo and himself as the change candidate.
"I'm going to do my very best to communicate as clearly and fearlessly as I can in face of the insults and attacks and bullying and bigotry that we've seen coming from my opponent," Clinton said on the Steve Harvey radio show last week.
Both rivals know that presidential debates are not an academic exercise -- often the winner is not the candidate who shows the clearest command of the facts but the one whose presence, body language and personality come across as closest to the popular understanding of presidential gravitas and bearing.
Trump is approaching the showdown with characteristic bravado -- ignoring the kind of secluded debate retreats most candidates favor. He hasn't, for example, practiced debating a stand-in for Clinton.
His blasé approach is worrying aides who fear his freewheeling style underestimates the magnitude of a presidential debate. The billionaire enters the clash claiming momentum in the polls but needing to address liabilities among female, and minority voters who would be crucial to piecing together a winning coalition.
Another question is which Trump will show up?
The GOP nominee could decide to adopt the more scripted persona he's displayed in recent weeks. But in the spontaneous environment of the debate stage, the unpredictable Trump could re-emerge along with the willingness to say things that more traditional candidates would abhor -- and which delight his admirers.
But Trump may be vulnerable to Clinton's attacks on his past unflattering rhetoric toward women. Clinton may also bring up his language on Mexican immigrants and African-American voters to suggest he's unfit to lead all Americans. She could try to goad him into errors to prove her claim that no one who can be "baited by a tweet" is fit to serve as commander-in-chief.
Trump has also never taken part in a one-on-one debate. The packed stage at the GOP primary debates often allowed him to bluster through critiques of his thin policy agenda and experience or to take time-outs while other candidates sparred.
But the concentrated spotlight at the 90-minute presidential debate -- with no commercial breaks -- makes it more difficult to get away with the vague, sweeping and untruthful statements with which he peppered the primary showdowns.
Still, the Clinton campaign is showing real signs of concern that Trump's method will simply blow up the format of the presidential debates -- and the way the media and audience evaluate who won.
"Donald Trump has pattern of repeating lies hoping no one will correct him," said Jennifer Palmieri, Clinton's communications director last week.
"Any candidate who tells this many lies clearly can't win the debate on the merits," she said. "His level of lying is unprecedented in American politics."
Trump's behavior and frequent refuge in falsehoods will also challenge the conventions of how debates are normally judged, placing intense pressure on moderator Lester Holt of NBC. The post-game spin will also help decide how this first of three debates influences the election.
"Historically, the debates have not overcome the fundamentals of the election," said Republican pollster Whit Ayers on CNN's new podcast "Party People." "That said, there have been debate moments that we can all remember that have galvanized the election and have led to one candidate doing substantially better."
Examples of debates changing the election include 1980 when Ronald Reagan performed well enough against Jimmy Carter to assure voters he could handle the demands of the presidency. In 2000, George W. Bush did the same against the more experienced Al Gore in a parallel of the commander-in-chief test that Trump is facing.
And back in 1960, the new medium of television emphasized the charisma of Kennedy -- who went into debate season one point behind Nixon -- but emerged with a four-point lead.
This year, if the debates are decisive, there are two possible outcomes. Either Clinton could triumph over Trump and effectively put the race away, given her current narrow lead in opinion polls. Or, if she stumbles and Trump surpasses a fairly low behavioral and policy bar, the billionaire appears to have the chance to turn the election into a cliffhanger or even forge ahead.
But first, he must avoid being caught in a huge error, since despite his notoriety, there will be many voters who have yet to see him in the political context.
"There were a lot of people who don't know him. who have never seen him perform before," Helwich said. "He will still be facing the first task of meeting audiences' expectations of what a president looks like."