Hillary Clinton is clinging to a lead in most national polls, but Donald Trump has been making up ground as they enter the kickoff presidential debate Monday with dramatically different expectations.
Mrs. Clinton, a lifelong politician’s wife turned politician, is hoping to show she is the only serious candidate. Mr. Trump, a novice politician who battered his way through the Republican primary race with insults and a lack of policy, will be at pains to prove he can behave on the biggest stage.
The 90-minute debate is projected to attract as many as 100 million viewers, but the real prize will be the tens of millions of undecided voters.
Mrs. Clinton would be the first woman to win the White House, and Mr. Trump would be the first without political or military experience.
Both candidates face unique challenges.
“I think Hillary Clinton needs to be more authentic and show her human side more, and I think that is the piece that is missing,” said David Paleologos, director of the Suffolk University Political Research Center. “There is a sense that everything is pre-tested, pre-polled, and has been reviewed by a number of top-level political advisers, and I think she has to cut through all of that.”
At the same time, the general consensus is that Mr. Trump needs to show voters — including suburban Republicans — that he is a reasonable person who has a firm grasp of the issues.
“I think Donald Trump has to appear presidential and in command of the topics that will be discussed, and he needs to be convincing but detailed in responses, as well as respectful,” Mr. Paleologos said.
Kevin Sheridan, a Republican Party strategist, said the expectations are higher for Mrs. Clinton than Mr. Trump, who will be participating in the first one-on-one debate of his political career.
“Hillary goes down if Trump remains calm, ignores her insults and is remotely presidential for 90 minutes,” Mr. Sheridan said. “Trump goes down if he can’t do the bare minimum of looking adult.
“Big if, but I’d put money on him in this exchange,” he said. “She’s on the Mount Rushmore of defective presidential candidates, so anything approaching normalcy against her wins the day.”
The debate is being moderated by Lester Holt of NBC News. Libertarian candidate Gary Johnson and Green Party candidate Jill Stein failed to qualify for the event because of poor polling.
The race turned nasty over the weekend after Mr. Trump floated the idea of inviting entertainer Gennifer Flowers — who had an affair with Bill Clinton in the 1970s — to the debate after learning that Mrs. Clinton had invited Mark Cuban, the billionaire owner of the Dallas Mavericks and outspoken Trump critic.
The Trump camp played damage control Sunday by saying Miss Flowers, who reportedly was open to idea of attending, would not be invited.
For months, Mrs. Clinton and Mr. Trump have been test-driving messages that they are likely to deploy on the debate stages.
Mrs. Clinton has tried to capitalize on her experience as first lady, U.S. senator and secretary of state by casting Mr. Trump as a policy lightweight who is too unpredictable to lead the nation and have his finger on the nuclear codes.
She also has called on Mr. Trump to release his tax returns, as every major presidential candidate since the 1970s has done, arguing that his reluctance shows he has something to hide.
Mr. Trump has tried to capitalize on being the outsider in the race by casting Mrs. Clinton as a part of the status quo that has done little to help working-class Americans and too secretive to be trusted as commander in chief.
Both lines of attack appear to be resonating with voters.
A Washington Post/ABC News poll of likely voters released Sunday showed that 33 percent of respondents said Mrs. Clinton was trustworthy and honest, compared with 42 percent for Mr. Trump.
More than half of the respondents said Mr. Trump is not qualified to be president and lacks the temperament for the job.
The survey showed that the lead Mrs. Clinton carried through most of the summer had all but evaporated, reflecting trends from other polls.
Eight in 10 voters said they plan to watch the debate.
Mr. Trump and Mrs. Clinton also are running neck and neck in a number of key states, including Ohio, Florida and North Carolina.
The tightening follows a tough few weeks for Mrs. Clinton, who suffered a pneumonia-related health scare the day after she described a broad swath of Mr. Trump’s backers as “deplorables.”
Mr. Trump, meanwhile, has faced questions about his use of money from The Trump Foundation, his refusal to release his tax returns and his tenuous relationship with the truth.
He also faced a barrage of criticism this month for falsely claiming that Mrs. Clinton and her 2008 campaign team started the “birther” movement, which asserted that Barack Obama was born overseas and therefore was ineligible to be president.