Under the Justice and Development Party AKP and Recep Tayyip Erdoğan, Turkey has become one of the most polarized countries in the world, and has undergone a significant democratic breakdown. This article explains how polarization and democratic breakdown happened, arguing that it was based on the built-in, perverse dynamics of an “authoritarian spiral of polarizing-cum-transformative politics.” Furthermore, I identify ten causal mechanisms that have produced pernicious polarization and democratic erosion. Turkey’s transformation since 2002 is an example of the broader phenomenon of democratic erosion under new elites and dominant groups. The causes and consequences of pernicious polarization are analyzed in terms of four subperiods: 2002–2006, 2007, 2008–2013, and 2014–present. In the end, what began as a potentially reformist politics of polarization-cum-transformation morphed into an autocratic-revolutionary one. During this process, polarization and AKP policies; the politicization of formative rifts that had been a divisive undercurrent since nation-state formation; structural transformations; and the opposition’s organizational, programmatic, and personal shortcomings fed and reinforced each other.