President Trump has been practicing with flashcards and prepping with former New Jersey Gov. Chris Christie before Tuesday's presidential debate

Behind the scenes: Top aides tell Axios he's been testing his attacks on the campaign trail for weeks, seeing what ignites his crowds or falls flat. One of the biggest themes Trump plans to drive home is his "tough guy" persona, which advisers see as an advantage with voters in key states.

Joe Biden has blocked off full days for mock debate sessions ahead of the Tuesday debate in Cleveland.

• Expect a big emphasis from Biden on the sad milestone the U.S. passed last week — the 200,000th U.S. death from COVID.
• While Biden plans to challenge Trump on any falsehoods, advisers say he won't spend the whole debate playing fact-checker.

Trump's team sees Judge Amy Coney Barrett as a vehicle to bait Biden into turning off centrist voters — if the president can goad Biden into attacking her.

• That's something Biden advisers have already said they plan to avoid.
• But Trump's team notes during past Democratic debates, Biden lost his temper.

Biden will counter Trump on the Supreme Court by focusing on how a 6-3 conservative court could be disastrous for the Affordable Care Act.

• Biden has had several long weekend sessions and some shorter weekday rounds.
• The informal practice sessions included staff peppering him with questions and massaging his answers.

Rep. Alexandria Ocasio-Cortez tells Axios it's important for Biden not to "demoralize" the base with a swipe at progressives:

• "We're working really hard to try to turn out young people, and it's just not helpful to decry people like myself or Bernie Sanders."

Between the lines: Here's what keepsthe strategists up at night ...

For Trump:

Overconfidence. Many people close to the president say they're worried he hasn't taken the debates seriously or prepared enough.

• "Presidents typically lose the first debate to a challenger," top Trump ally Rep. Matt Gaetz (R-Fla.) tells Axios.
• Trump sees Bidenas someone he can bulldoze. But Trump's team has warned him that Biden is a seasoned politician.

Policy. One of Trump's big misses of the summer was his failure to lay out what his second-term agenda would look like. He did that during his convention speech, but this time he won't have a prewritten speech or teleprompter to rely on.

• Trump has always struggled with policy debates, instead preferring to ramble and generalize. But Fox News moderator Chris Wallace is a seasoned Trump interviewer, and he knows how to force Trump to be direct.

Attacks on the moderator. Many Republicans still shudder at the memory of Trump's vicious attacks on Megyn Kelly, then of Fox News — something that stuck with viewers for months.

Downplaying the coronavirus. Trump's team recognizes that the president's biggest weakness is his handling of the coronavirus and the casual way in which he has seemingly minimized the number of people who have died.

• This is the areain which they have tried to prep him the most. But Trump's refusal to admit he's done anything but a fantastic job presents a real problem.

For Biden:

Gaffes. Confidants believe the main risk for Biden is misspeaking, transposing numbers or seeming to lose his train of thought.

• If Biden does have a verbal misstep, their plan is to compare it to whatever mistakes Trump makes.

Temper. In some of his interactions with voters on the trail, Biden has shown flashes of anger.

• His challenge will be responding to Trump forcefully, without losing his cool.

Verbosity. Biden, who overcame stuttering as a child, well knows — and frequently chides himself — for going too long.

• He also tends to take detours on his way to the point he is trying to make.
• He's also a creatureof decades spent in the Senate, and some of his parliamentary verbiage is better understood in the cloakroom than in American living rooms.
• He has seemed to meander in the past by mentioning old colleagues and mentors, like in a CNN town hall when he name-checked the late Sens. Mike Mansfield and Ted Kennedy.

Deference to the moderator — something Biden did during primary debates.

• The danger is inadvertently ceding ground to Trump.

Taking the bait. Trump's preferred ways of getting under Biden's skin include suggesting he's lost a mental step because of his age (Biden is 77; Trump is 74) or going after Biden's son, Hunter. 

Go deeper ... Debate commission co-chair: We don't expect moderators to fact-check candidates