Donald Trump and Hillary Clinton hurtle toward their first debate Monday night, facing crucial tests about whether the often-brash Republican nominee can demonstrate the temperament and policy expertise to serve as president and whether Clinton can overcome trust questions with voters that have dogged her for years.

Trump’s allies said the real-estate mogul is eager to address substantive policy issues, even as top campaign officials on Sunday worked to tamp down the potential for off-stage fireworks initiated by Trump suggesting on Twitter that Gennifer Flowers would attend the showdown at Hofstra University in Hempstead, N.Y. Flowers has said she had an affair with Bill Clinton when he was Arkansas governor.

Clinton’s aides, meanwhile, worried publicly that Trump, a wealthy TV star and real-estate developer making his first bid for public office, would be held to a lower standard on the debate stage than Clinton, a former secretary of State who has spent decades in public life.

“I’m very concerned that Donald Trump will be graded on a curve,” Clinton campaign manager Robby Mook said Sunday on CNN’s State of the Union.

“Just because he doesn’t fly off the handle in the middle of the debate doesn’t mean that he’s prepared to be president of the United States,” he said. “He needs to have coherent answers to the questions. He needs to demonstrate a command of the issues. And he needs to roll out specific plans about how he’s going to make life better for Americans.”

Despite Trump’s suggestion he would invite Flowers to the event, Kellyanne Conway, his campaign manager, said there’s “no plan” for Trump to raise Bill Clinton’s past infidelity during the debate.

“But the fact is that he has every right to defend himself. You know, he’s always, constantly attacked, and then the moment he counterpunches, then people are just shocked that he would do that,” Conway said of Trump. “But he will answer the questions. We certainly hope that the questions go to policy.”

The stakes are high for Monday night’s showdown, the first of three debates in an increasingly tight race for the presidency. Both camps expect high viewership with a TV audience that could top the record 80 million who watched Jimmy Carter and Ronald Reagan debate in 1980.

A new poll shows the two meeting on the debate stage Monday in a near dead heat.

Clinton, the Democratic nominee, has the support of 46% of likely voters and Trump 44% in a Washington Post-ABC News poll released over the weekend. Libertarian Party nominee Gary Johnson and Green Party candidate Jill Stein were at 5% and 1%, respectively.

The poll also shows 17% of registered voters still undecided, six weeks before Election Day.

“There’s still a large number of people who could sway this election,” said G. Terry Madonna, a political scientist who oversees polling at Franklin & Marshall College in Lancaster, Pa. “A one-liner that sticks, a gaffe, something that they do that's provocative. All of that has the possibility of changing the dynamics of this race.”

Monday’s 90-minute event will kick off at 9 p.m. ET and will be moderated by NBC’s Lester Holt, who is expected to touch on broad themes of national security, economic growth and the country's direction. In the lead up to Monday's face-off, Trump has maintained that it would be inappropriate for Holt to fact-check candidates' statements during the debate — a contention repeated Sunday by his running mate, Indiana Gov. Mike Pence.

"We need to hear from these two candidates, and I hope and trust the moderators will just facilitate that," Pence said on CBS' Face the Nation.

By all accounts, Clinton has spent weeks preparing for Monday night, including participating in mock debates in recent days. She took several days off the campaign trail in the last week to prepare.

Trump and aides have said little about his debate preparation but say he is not following traditional procedures, opting to bat around ideas with aides at Sunday gatherings and review Clinton's past debate performances.

Trump campaigned nearly every day over the past week and took to social media to bait Clinton, including floating the prospect of a debate invitation to Flowers, whose public discussion of an affair with Bill Clinton threatened his 1992 bid for the presidency. Trump did so after rival businessman Mark Cuban said he planed to occupy a front-row seat at the debate in support of the Democratic nominee. Cuban and Trump spar often.

While Flowers said over the weekend she would attend the debate, Trump aides said they don't plan to have her there. "Gennifer Flowers will not be attending the debate tomorrow night," Pence said flatly on Fox News Sunday. Conway said Trump raised the specter of Flowers' attendance to "remind people that he's a great counter-puncher."

Mook, Clinton's campaign manager, sought to seize on the Flowers episode Sunday to portray Trump as unfit for the role of commander in chief. "I think the fact that Donald Trump is spending the hours before this debate on this sort of thing is indicative of the kind of leader he would be," Mook said on CNN.

Contributing: David Jackson