Do NBC’s hosts have such a question up their sleeves? Campaigns are brainstorming to prepare for such a snap-judgment moment that could be one of the more powerful visual takeaways of the debate.

Among the potential questions that could be a raise-your-hand moment: Do you think President Trump should be impeached? Is Mr. Trump a racist? Should prisoners have the right to vote? Should Mr. Trump be prosecuted after leaving office? Should the entire 2017 Trump tax bill be repealed?

[18 questions. 21 Democratic candidates. Here’s what they said.]

Who can jump into the top tier of candidates?

Many of the Democrats running are unknown to much of the country. They will be trying to make positive, memorable impressions. The biggest hope of all: to vault themselves into the top tier of 2020 candidates.

It is a challenging feat on a crowded stage when you have limited time to speak. But it is possible to break out of a lower tier. Just ask Carly Fiorina, the former chief executive of Hewlett-Packard. In the 2016 presidential primary campaign she was relegated to an “undercard” debate for lower-polling Republican candidates in the first round, but broke through and later landed on the main stage.

“I always had a set of points — not 20; four or five — that I needed to make in the course of the debate,” she said in an interview. “If you know what those are and you are in the moment, then you are looking for the moment when you can make that point.”

But, she cautioned, “No one is going to dominate the airwaves like Donald Trump did and does. So don’t try.”

[See what issues our readers said they would most like to hear about in the first round of Democratic debates.]