In this chapter, I argue that a key difference between Argentina and Chile that caused the divergent outcomes in presidential power is the extent to which presidents in both countries were able to gain working majorities in congress. In the first part of this chapter, I describe how Argentine presidents were often able to concentrate power through their de facto majorities for many years in congress, in which it was especially likely for Peronist presidents to benefit from de facto unified government. In the second part, I show how Chilean presidents had significantly more difficulty achieving majorities in congress, and how this lack of a party majority prevented presidents from concentrating power. In this chapter, I also show how the parties of Argentine presidents were significantly more disciplined than the parties of Chilean presidents. I make a general observation that party cohesion increases presidential power, and describe three general mechanisms to reduce presidential power via the reduction in party discipline.