Political ideology in the United States is typically described as a spectrum. This metaphor implies that the people who place themselves along the spectrum differ in degree from each other; an individual who places themselves all the way on the left of the spectrum, is an extreme version of another closer to the middle. Political polarization and elite extremism are on the rise in the United States (e.g., Finkel et al., 2020), and attention to political polarization has fueled efforts to understand the extreme right (e.g, Forscher & Kteily, 2020), and driven attempts to identify whether the extreme left may or may not share authoritarian tendencies with those on the extreme right (Conway et al., 2018; Costello et al., 2021; Badaan et al., 2020; Nilsson & Jost, 2020). The central focus of psychology on the extreme Left has been on Left-wing authoritarianism¬—whether it exists, is appropriately named, or logically possible (Conway et al., 2018; Costello et al., 2021; Badaan & Jost, 2020; Nilsson & Jost, 2020). However, this approach sidesteps a longstanding distinction that exists among politically left-leaning individuals–that between Leftists and Liberals (see Menand, 2021). While Leftists explicitly describe themselves as completely separate from Liberals¬, who they claim cooperate with existing institutions and seek insufficient social change (Ture, 1966), Liberals may more easily see themselves as part of a larger left-leaning political group, such that they express surprise and even anger when Leftists do not support their political agenda (Capeheart, 2020). It is the aim of this paper to investigate the psychological differences between Leftists and Liberals (i.e., in terms of ideology, morality, political preferences, and judgments of group boundaries) to further our understanding of how these two historical groups may differ and interact, and help us understand political ideology, identity, and radicalism, more broadly.