WASHINGTON – It is Steven Spielberg’s singular achievement to have made a heroic movie about compromise and petty corruption. In “Lincoln,” he puts a tight frame on the Cabinet meetings, legislative debates and backroom confrontations where the final, decisive battles of the Civil War were fought. Combat determined the outcome of the War Between the States. Politics determined its meaning, culminating in passage of the 13th Amendment. Spielberg focuses on the peculiar process that brought down the peculiar institution. It is an epic staged in cramped, Victorian rooms.

Better than any other, the movie captures President Lincoln’s awkward, shuffling, distinctly democratic greatness. The humanity, frailty and aching introspection. The shrewdness, decisiveness and ferocious will. It is the democratic faith that exceptional leaders can be found among common folk. But it is still shocking that such a leader should be Thomas Lincoln’s son.

While Lincoln is the center of the movie, its subject is politics – the race to pass a constitutional ban on slavery before the readmission of Southern states that would have doomed the effort. Lincoln’s critics sometimes accuse him of indifference to the law and the Constitution. In fact, he was a legalist to the core. As the Civil War came to a close, Lincoln knew that a wartime measure such as the Emancipation Proclamation could easily be undone if it were not reflected in the text of the Constitution.

However venerable that document, the process it produces is not always attractive. Lincoln plunged into a vote-gathering effort that stopped just short of bribery. Politics, in “Lincoln,” is a mix of motivations, noble and base. With the right leadership, the sum of politics becomes much larger than the flaws of its participants.

This is consistent with the realism of the Constitution’s framers, who assumed the general pursuit of interest and attempted to channel it toward public purposes. But the channeling is helped by good leaders.

Two moral leaders in “Lincoln” vie for our sympathy: the radical abolitionist Thaddeus Stevens and Lincoln himself. It is a measure of the film’s ambition and complexity that the purer, more satisfying moral position – Stevens’ admirable (and personal) embrace of social equality between black and white – would have led to the 13th Amendment’s defeat. Stevens ensures passage by publicly tempering his deepest convictions. But by dividing our moral sympathies from our pragmatic judgments, Spielberg conveys something of Lincoln’s burden. While justice is not defined by the majority, it can’t be pursued without support from the majority. So Lincoln tacks back and forth, willing to compromise on almost everything – except his destination. For Lincoln, all politics is barter – but done in service to a purpose beyond barter.

The union would be well served today by herding all 535 of its legislators in for a screening of “Lincoln.” The issues they face are less momentous than slavery, but momentous enough for discomfort. They might take away a greater appreciation for flexibility and compromise. They should also note that the dramatic culmination of the movie is a roll call – a list of forgotten legislators whose hesitant, conflicted choices were as important as the outcome of battle. Their shared profession may lack in dignity but not in consequence.