Romein held Marxist views and was active within the Communist Party of Holland (CPH) from 1917 onwards, initially as a secretary for the communist parliamentarian Willem van Ravesteyn, then as a high-ranking editor of the party's daily "De Tribune". When internal struggles led to a Moscow-backed "palace revolution" in 1925, Romein sided with Van Ravesteyn and David Wijnkoop, and as a result was forced out of the "Tribune"'s editorial board. Expulsion from the party for continued support of Wijnkoop followed in 1927, ending Romein's direct involvement in politics.