The test of a movie, I always think, is not so much the impact it has on one in the cinema, but whether it lives on in one’s mind in the days and weeks afterwards. Spielberg’s Lincoln, which we saw last night, passes that test with flying colours. There are lots of reasons for admiring the movie, and most of them have been extensively rehashed by critics more knowledgeable than me, so I won’t dwell on them here, except to say that Daniel Day-Lewis’s performance as Lincoln is truly awe-inspiring in capturing the greatness and the humanity of the man: his inner confidence, his conversational style, his unique combination of patience and impatience, his combination of realism and idealism, his wit. And, above all, his weariness.

And who would have thought that you could make a Hollywood blockbuster out of 150 minutes of pure dialogue? But actually the film’s dialogue is a work of genius. Or, more precisely, of a genius, name of Tony Kushner, who strove not just for wit and sparkle, but also for historical accuracy. He worked with the 20-volume OED by his side, checking the historical accuracy of the terms used by the characters. The only made-up word, he told the Boston Globe, was “grousle” — used by Lincoln in exasperation at the cavilling of his cabinet: “You grousle and heckle and dodge about”, he expostulates, “like pettifogging Tammany Hall hucksters.” The dialogue I enjoyed most, however, came not from Lincoln but from Thaddeus Stevens (played by Tommy Lee Jones), whose withering scorn for his political opponents left this viewer awestruck with admiration. (I used to be a TV critic, and so am a connoisseur of invective.) When he moderated his radical stance (he was a fervent believer that all men are created equal) for pragmatic reasons to the statement that “all men are equal before the law”, he was challenged by George Pendelton of Ohio on whether he believed that all men were equal. “You”, he said, staring at Pendleton, “are more reptile than man, George, so low and flat that the foot of man is incapable of crushing you.”

What’s most admirable about the movie is its willingness to embrace the complexity of the story of the Thirteenth Amendment. Politics is always a messy business, and politics in time of war is even messier. What the movie brings out brilliantly, though, is how politics is the art of the possible. It shows Lincoln achieving a supremely worthwhile end (enshrining the outlawing of slavery in the Constitution) by dubious – but not illegal — means. It leaves one thinking romantically about Churchill’s trope about democracy being “the worst system — except for all the others”. And shaking one’s head at the mess that Lincoln’s successors have made of his legacy.