President Obama has given the new film Lincoln a thumbs-up, the film’s screenwriter, Tony Kushner, said Thursday night at Newsweek and The Daily Beast’s Hero Summit in Washington, D.C.

Kushner would know. Just before arriving at the summit, he had dashed across town from a private screening he attended with Obama and the film’s director, Steven Spielberg, among others, at the White House.

Kushner joined moderator Tina Brown on a summit panel about the making of the film, saying he thought Obama “really liked it." The president's entourage also "seemed to like it," he said. "They all stood up.” Then he joked, “Maybe they do that every time.” Clearly having an unusual evening, he added with a laugh, as if to explain his somewhat harried state, “I just literally walked out of the White House. I couldn't find the limo.”

Kushner, who won a Pulitzer Prize for his play Angels in America, said he wrote three drafts of the Lincoln script, which ultimately zoomed in on the president’s life during the passage of the 13th Amendment abolishing slavery. The film is based in part on the book Team of Rivals: The Political Genius of Abraham Lincoln, by Doris Kearns Goodwin.

Kushner said he “picked over words” in the final script with actor Daniel Day-Lewis, who plays Lincoln in the film, “trying out different sentences—what if we did this, what if we did that.” Kushner called the back-and-forth a lot of fun.

When it came time to start filming, however, Day-Lewis explained to Kushner that it was time to move into a new mode. “He said, ‘I hope you won’t feel bad when I stop speaking with you on the set. At that point, I can only have a conversation with Steven.’”

Kushner said, “We texted.”

Day-Lewis put a tremendous amount of time into preparing for his character, said producer Kathleen Kennedy, who was also on Thursday night’s panel, following a special screening of the film to wrap up The Hero Summit. Noting that the actor is generally “very reluctant to talk about his process,” she said, he “spent a year working on the character before filming.”

Day-Lewis “read a great deal about what Lincoln might have sounded like,” Kennedy said. In practicing Lincoln’s voice, the actor sent secret recordings to Spielberg. “The two of them kept that conversation very private. It was something that was so personal to Daniel," she said. "He knew that once he found that voice, he would need to completely inhabit it.”

The first day she saw Day-Lewis in costume, it was “completely mesmerizing,” Kennedy said. “He put the top hat on, and he just became Lincoln. It was all in the behavior. That was another thing he spent a great deal of time on,” she said, noting that Lincoln was exhausted and stooped-over at this stage in his life, often shuffling throughout the White House.

Kennedy said one of the many challenges of the film was the casting, which involved 148 speaking parts. One of the actors in the film, Gloria Reuben, was also on Thursday night’s panel, describing her role as dressmaker to First Lady Mary Todd Lincoln, played by Sally Field in the film.

“She was born into slavery,” Reuben said of her character, Elizabeth Keckley. “Her biological father was her master.” Keckley eventually bought her own freedom, becoming a successful seamstress and a confidante to the first lady. “I literally jumped for joy when I found out I was going to play her,” Reuben said, noting that Keckley represents “all of these countless stories woven into this one woman’s story.”

When Brown asked if the filmmakers wanted to make a statement on modern politics, Kennedy called the film “a celebration of democracy,” adding, “that’s what we were really trying to show—the political process is something to be celebrated.” Kennedy said the filmmakers had decided not to release the film before the presidential election this year because “we didn’t want it to be used in a political way.”

Kushner said he talked personally with Obama about the film on Thursday night and that the president “really knows his Lincoln.”

Kushner also said he felt that Obama’s decision to express support for gay marriage was “very Lincolnian.” He said, “I think it was handled with absolute strategic and moral perfection. It arrived at exactly the right moment. As my husband said to him tonight, it was a life-changing moment when the president of the U.S. said that.”