Social democratic parties have no choice but to adopt a big-tent philosophy, one that unabashedly embraces other center-left political parties and progressive organizations. Europe’s progressive forces can only forge a stable majority if they transcend their party boundaries. It may not be comfortable for social democrats to do this, and it certainly won’t be easy. But it is necessary: Only social democrats have the organizational muscle, political maturity, and roots in the working class to forge such a coalition.