Aaron Bady argues that, by focusing on the negotiation for the Thirteenth Amendment, the film creates an "artificial sense that more is at stake in a single congressional bill than there actually was":
As Eric Foner pointed out when he was asked about the movie, if it hadn’t passed when it did, Lincoln had pledged to call Congress into special session in March; “[a]nd there, the Republicans had a two-thirds majority and would ratify in a minute…It’s not this giant crisis in the way that the film’s portraying it.”
Bady goes on to complain that the film makes it seem "that black people had no effect on the politics of slavery and emancipation (except insofar as they inspired the people who mattered)" - an important nuance given that slavery was in its death throes not primarily because Lincoln ratified its end but because slaves themselves were seizing freedom. Along those lines, historian Kate Masur wishes the film included the throngs of fugitive slaves who fled to Washington, DC:
By 1865 — Mr. Spielberg’s film takes place from January to April — these fugitives had transformed Washington’s streets, markets and neighborhoods. Had the filmmakers cared to portray African-Americans as meaningful actors in the drama of emancipation, they might have shown Lincoln interacting with black passers-by in the District of Columbia.
Black oral tradition held that Lincoln visited at least one of the capital’s government-run “contraband camps,” where many of the fugitives lived, and was moved by the singing and prayer he witnessed there. One of the president’s assistants, William O. Stoddard, remembered Lincoln stopping to shake hands with a black woman he encountered on the street near the White House.
Douthat, on the other hand, defends the film:
The problem is that every historical film has to “ignore the big picture,” because actual history just too big to fit the screens and stories that we have. The question isn’t whether to edit; it’s where and how and what, and how to balance the requirement to win a contemporary audience with the obligation to do justice to the actual historical record. The justice that “Lincoln” does to its complicated subject is necessarily flawed and incomplete. But I can see why its makers made the choices that they did, and I think the results, while imperfect, are more impressive than many films about the foreign country of the past.