The SDP entered the elections again in July 1918, winning two seats that were occupied by Willem van Ravesteyn and Wijnkoop; Wijnkoop assumed the leadership of the party. The SDP formed a revolutionary parliamentary party with the League of Christian Socialists and the Socialist Party, both of which had one seat. In 1921 Willy Kruyt, the MP for the League of Christian Socialists, joined the SDP while the MP for the Socialist Party left the revolutionary parliamentary party.
