Watch the debate here:
After the debate, we'll have analysis from Simon Maloy, Gary Legum and more Salon.com writers.
[UPDATE: Post-debate analysis]
Preparing for the debate? Here are a few articles you may have missed:
Here's a look at what's at stake, according to the Associated Press:
With millions watching and the American presidency on the line, tonight's must-see showdown pits Democrat Hillary Clinton's call for steady, experienced leadership against Republican Donald Trump's pugnacious promises to upend Washington.
The 90-minute televised debate comes six weeks before Election Day and as early voting is already getting underway in some states. Despite Clinton's advantages, including a sophisticated get-out-the-vote operation and a favorable electoral map, the race is exceedingly close.
For Clinton and Trump, the first of three debates is a crucial moment to boost their standing with voters who view both candidates negatively. Clinton struggles with questions about her trustworthiness, while Trump has yet to prove to some voters that he has the basic qualifications to serve as commander in chief.
National interest in the race has been intense, and the campaigns are expecting a record-breaking audience to watch Monday's event at suburban New York's Hofstra University. Both candidates were continuing intensive debate prep nearly until air time.
Clinton aides spent the days leading up to the debate appealing for the media and voters to hold Trump to a higher standard than they believe he has faced for much of the campaign. Their concern is that if the sometimes-bombastic Trump manages to keep his cool onstage, he'll be rewarded — even if he fails to flesh out policy specifics or doesn't tell the truth about his record and past statements.
Clinton campaign manager Robby Mook said Monday that he was "concerned that Trump is going to continue to lie."
On the other side, Kellyanne Conway, who took over as Trump's campaign manager last month, accused Clinton's team of engaging in "very public and very coordinated attempts to game the refs." She said the effort reflected worries among Clinton supporters about the Democrat's debating skills.
Trump and Clinton have spent months tangling from afar and are divided on virtually every major issue facing the country. They're sure to face questions about domestic terrorism and police shootings given recent incidents in New York, North Carolina and elsewhere.
The centerpiece of Trump's campaign has been a push for restrictive immigration measures, including a physical wall along the U.S.-Mexico border and an early proposal to temporarily bar foreign Muslims from coming to the U.S. But he's been less detailed about other ideas, including his plan for stamping out the Islamic State group in the Middle East, and Conway suggested he'd be similarly reticent in the debate.
"You will get his view of how best to defeat the enemy — without telling ISIS specifically what it's going to be," Conway said.
Clinton, a former senator and secretary of state, is banking on voters seeing her as a steady hand who can build on the record of President Barack Obama, whose popularity is rising as he winds down his second term in office. She's called for expanding Obama's executive orders if Congress won't pass legislation to overhaul the nation's immigration system and for broader gun control measures. Overseas, she's called for a no-fly zone in Syria but has vowed to keep the military out of a large-scale ground war to defeat the Islamic State group.
For Clinton, victory in November largely hinges on rallying the same young and diverse coalition that elected Obama but has yet to fully embrace her. Mook told "CBS This Morning" that she understands she still needs to earn voters' trust.
"When she's had the opportunity to talk about not just what her plans are to make a difference in people's lives, but how this campaign is really part of a lifelong mission to fight for kids and families, she's done really well," Mook said.
Former President Bill Clinton planned to travel to the debate with his wife, but it was unclear whether he planned to watch the event from inside the debate hall.
Trump has tapped into deep anxieties among some Americans, particularly white, working-class voters who feel left behind in a changing economy and diversifying nation. While the real estate mogul lacks the experience Americans have traditionally sought in a commander in chief, he's banking on frustration with career politicians and disdain for Clinton to push him over the top on Election Day.
Trump was often a commanding presence in the Republican primary debates, launching biting personal attacks on his rivals. But at other times, he appeared to fade into the background, especially during more technical policy discussions — something he'll be unable to do with just two candidates on stage.
Clinton has debated more than 30 times at the presidential level, including several one-on-one contests against Obama in 2008 and Vermont Sen. Bernie Sanders in 2016. But Monday's contest will be her first presidential debate against a candidate from the opposing party.