sentences:  Presidents Álvaro Obregón (1920–1924) and Plutarco Elías Calles (1924–1928) were elected on a PL ticket and in 1922 the PL managed to defeat the Liberal Constitutionalist Party (PLC) in congressional elections, becoming largest party in the Congress of Mexico.Competition with rival parties, including the PLC, the National Cooperativist Party (PNC), the Mexican Communist Party (PCM), the National Agrarianist Party (PNA) and the National Anti-Reelectionist Party (PNA) was often violent, the government usually supporting the PL.After the assassination of Obregón, who was recently elected, in 1928 the party's power started to decline.