The stakes are a little different for each of them, too.
For Clinton, the second debate is an opportunity to sustain the momentum she's drawn from the first. Polls this week showed the former secretary of state with leads nationally and in key swing states.
For Trump, Sunday's debate will be a mulligan of sorts. Clinton was widely seen as the winner of the first debate, and Trump has been at the center of controversy ever since.
Here's how each candidate is preparing for round two as of Wednesday.
Clinton off the trail
The Democratic nominee is off the campaign trail ahead of Sunday's debate, leaving media appearances and public rallies to her deep bench of high-profile surrogates, including her immediate family, the first family and Al Gore. Clinton does, however, have fundraisers slated for Wednesday and Thursday, including one that will be open to cameras.
Advisers say the reason behind the decision is simple: the debate carries far greater importance than a standard campaign event. The first debate was viewed by more than 80 million, far more than the audience for any rally.
Clinton's top takeaway from her first debate with Trump was that preparation matters. So ahead of the contest at Washington University, Clinton will hunker down with a select group of aides later this week to refine her attacks on Trump and prepare for the added level of difficulty created by a live audience that asks questions.
Clinton is spending Wednesday preparing for the town hall debate at her home in Washington.
John Podesta, the campaign chairman, Jake Sullivan, Clinton's top policy adviser, and Ron Klain and Karen Dunn, two top members of Clinton's debate team, were all seen entering her home. The small group of aides were joined by Sara Solow, Kristine Costa and Tony Carrk, all members of the small group of aides working with Clinton ahead of Sunday's debate.
Podesta raised the stakes on Clinton's debate performance in a conversation with reporters, arguing that the format is natural for Clinton and bad for Trump.
"She is very used to the format. She likes it. She likes answering questions from individual citizens. She listens hard, she relates to people," Podesta said. "And that is a format that Donald Trump isn't as used to. And so we will see. I think it is a natural format for her. She likes engaging with people."
Clinton has not done any mock town hall debates yet, according to sources with knowledge of her debate preparations, but the plan is to do mock debates later this week. Philippe Reines, Clinton's longtime aide and defender who played Trump ahead of the first debate, will continue in the role and people close to him have said he worked to refine his Trump impersonation after the first contest.
Reines was not seen entering the home Wednesday.
Trump mocked Clinton taking time off the trail to prepare for the first debate, which was held late last month in Hempstead, New York. It prompted Clinton to deliver a retort she has since re-used in stump speeches.
"You know what else I prepared for?" Clinton said. "I prepared to be president."
Trump slates pre-town hall town hall
In contrast to Clinton, Trump will continue to greet supporters at campaign events prior to Sunday's debate. He has a pair of events scheduled for Wednesday in Nevada.
Trump will also participate in a town hall event on Thursday in Sandown, New Hampshire. It will be a tuneup of sorts for the debate, which will be a town hall format.
In the meantime, Trump's top aides are pushing the message that the Republican nominee will be prepared, something critics say was lacking in the first debate.
Trump campaign manager Kellyanne Conway told MSNBC on Wednesday that the candidate is "preparing constantly."
"Mr. Trump will be ready," the campaign's communications director Jason Miller said on CNN's "New Day."
Both Conway and Miller agreed that the second debate's town hall format will be conducive to Trump's style, but not Clinton.
"He has gotten very excited about the format," Conway said. "The town hall format is really a sweet spot for him."