http://the12.squarespace.com/james-bratt/2012/12/7/history-war-at-the-movies.html

Turns out that choosing Team of Rivals as resource (actually, selecting out of its 750-page narrative the bare thirty that cover the Amendment process) was a major interpretive choice that will likely seal the public’s understanding of Lincoln and the abolition of slavery for a long time to come. And will seal it on a false note. For as Lincoln’s critics point out, slavery was already a dead horse by the time (January 1865) the film starts rolling, and was so by virtue of actions undertaken by the slaves themselves. For three years they had been leaving their plantations, flocking to the advancing Union armies, enlisting in those armies to the tune of 200,000 men, sometimes dividing up Ol’ Massa’s lands for themselves, and in general creating a huge threatening cloud on the horizon of the moderates, like Lincoln, who were in charge of the Northern war effort. This was the urgency, not some (false) deadline for getting the text of the Amendment through Congress by the end of the month. The next Congress could have convened in March with a two-thirds majority of Republicans and no lame-duck Democrats to buy off—the horse-trading that the movie entertainingly follows.