Section 2 of the Voting Rights Act (VRA)—the crucial provision banning racial vote dilution—does not mention racial polarization in voting. Nor does polarization feature prominently in the list of factors included in the Senate report accompanying the Act; it is addressed by just one of the list’s ten or so items. Nevertheless, thanks to the Supreme Court’s epochal 1986 decision construing the Act, Thornburg v Gingles, polarization is “the undisputed and unchallenged center” of vote dilution law. It accounts, in fact, for two of Gingles’s three preconditions for liability: a “minority group must be able to show that it is politically cohesive” and also “must be able to demonstrate that the white majority votes sufficiently as a bloc.” Polarization is simply the difference between these quantities: minority support for a minority-preferred candidate minus white support for the candidate.