WASHINGTON (AFP) - Who is going to win? Who is going to choke? The pressure is intense for Republican Donald Trump and Democrat Hillary Clinton - phenomenally different candidates - who clash in their first debate on Monday.
Stakes are as high as they get since there are just six weeks until the November 8 election. Polls show a close race, with Clinton, 68, enjoying an edge.
As many as 90 million Americans, some estimate, will be glued to their television to catch the showdown.
Many analysts say debates usually don't win a candidate the election but can well lose it for them. A single sentence, or the slightest slip, can do serious damage.
Plenty of American voters will have made a decision by now, to be sure. Most have.
But nine percent by some estimates still don't know who to vote for, after a long campaign in which bitter attacks have often replaced substance.
And this year has been like none in the past, with Trump, 70, using social media around the clock in combative fashion, while often
making mistakes, misstatements and blunders without troubling his
On Saturday, the New York Times endorsed Clinton, who ahead of the debates has been cloistered with aides and her papers at home in Chappaqua, north of New York, even practicing with relatives playing Trump.
She has been focusing on his psychological profile, with a goal to get Trump to crack, to show that he can't control himself and lacks the even-handed temperament a president needs.
If he reacts by attacking, Trump also risks losing women's votes; he already has a harder time with women voters, and they make up 53 per cent of those who turn out. And any slip is sure to be a TV news sound bite.
Clinton's campaign released a long list of lies it attributes to Donald Trump ahead of the debate.
Trump in turn says preparations are "going very well," trying to at least appear relaxed. Friday he won the endorsement of former conservative rival Senator Ted Cruz.
Trump took Friday to prepare, and still had to work Sunday on the debate. But he continues with campaign rallies on other days, including Saturday night in Roanoke, Virginia.
Trump seems unwilling to train with a Hillary stand-in. But he has watched videos of his opponent in previous debates.
Supporters in Roanoke said they hoped Trump could keep his cool.
"I expect him to be more presidential but still tough," said Amanda Phillips, 36, and a social worker. She said she was "not 100 percent for the wall (with Mexico), and hopes Trump will be "more humane and not too hardcore."
Clinton, making her second presidential bid, is an old hand at debates and considered solid. In some ways, she may have more to lose.
After almost 40 years of public service, she is very well versed on the issues, and 88 percent of Americans believe she is smart.
But 65 percent say they do not find her honest. And 52 percent have a negative opinion of a woman they see as cerebral, distant or cold.
Her image has been sullied by Trump attacks over her email scandal, the Clinton Foundation's alleged pay-to-play donations, and her ties to Wall Street.
"Be yourself and explain what motivates you," President Barack Obama suggested to his former secretary of state, who as president would carry on the legacy of his two administrations.
Runningmate Tim Kaine has said of Clinton: "When the spotlights are at the brightest and the pressure is the most intense, that's when she brings her A-plus game."
Trump has not yet experienced a presidential debate: 90 minutes of intense questioning, with only one opponent and a moderator, who on Monday will be NBC news anchor Lester Holt.
But that does not worry the former reality TV star. He is good on his feet, and unpredictable, more comfortable in the limelight than on issues. He has promised to be "very respectful" with Clinton.
Trump is still perceived more negatively than Clinton: 61 per cent of Americans have a negative view of him, many saying they are put off by his personality and aggressiveness.