Brexit

As the British bicker over just how to leave the European Union, along comes a primer on how the 2016 vote for Brexit went down. The featurelength docudrama captures machinations on both sides, but focuses on the “Vote Leave” campaign and its little-known chief strategist. Benedict Cumberbatch is all in as the slight, balding Dominic Cummings, who eked out a narrow, unexpected victory by stoking racial resentments and using social media to stir up groups of potential voters no one had targeted before. Just don’t count on this being the definitive account. Saturday, Jan. 19, at 9 p.m., HBO