The book is scheduled to be published in early 2018.

In a joint telephone interview, Mr. Halperin and Mr. Heilemann spoke about why people will still be reading their book 50 years from now, and why they won’t ask Alec Baldwin to audition for the role of Mr. Trump in the mini-series. The following conversation has been edited and condensed.

Campaign reporting has changed since you published “Game Change.” There are new online outlets and every twist and turn is reported in real time. Is there that much that we don’t know, or any fresh ground to cover in reliving the 2016 campaign?

MR. HALPERIN I dispute the premise a little bit. More stuff comes out now on one level because of Twitter and other social media, but the fundamental principle, what we tried to achieve with “Game Change” and “Double Down,” remains the same. There’re people reporting on a lot of stuff, but the parade moves on so quickly that there’s still plenty of room to double back and look for stories and answers to things that you can’t get in real time.

The political news cycle is so punishing and relentless these days — journalists and citizens can barely keep up with new revelations. What value do you think there is in re-examining the campaign?

MR. HEILEMANN If you think again about the 2016 race, there are huge questions. Even now, if you think about what is going on in the political arena today, people are asking: What was the role of WikiLeaks in the campaign? Was the Trump campaign collaborating with the Russians? Why did [F.B.I. Director James] Comey do what he did? All those questions, people are talking about them right now. Despite all the coverage, we don’t know the answers to those questions. We think there’s still an awful lot to write about here.

Who would you cast to play Trump in the HBO mini-series, if Alec Baldwin isn’t available?

MR. HALPERIN We’re not prepared to discuss that yet, that will be done in conjunction with Playtone and HBO. But as great as Alec Baldwin is, the idea behind this is less caricature, and more interesting dramatic portrayal that’s not a cartoonish caricature.

So much has happened since the election, and since Inauguration Day, that will color the way readers and viewers view the campaign in hindsight. Will you nod to recent events in your book?