Mudge defines “left” parties as mass-based center-left parties that claim to pursue equality for the underrepresented in society. The UK Labour, German SDS, Swedish SAP, and US Democratic Party are compared from the late 1800s to the 1990s. The inclusion of the Democratic Party is artfully handled in its treatment as an organization that became “left” when it converged with its European counterparts through Keynesianism. This is explained through the Polanyian moments of the 1930s and 1970s, intraparty struggles for dominance, and transnational networks of politicians and economists. Party experts’ trajectories are contextualized within shifting relationships between social fields: economic, political, cultural, and bureaucratic.