The main way in which this has happened is through an increase in the power of the judicial branch. The presidency has also increased in power a great deal in the last hundred years.
The presidency had already started increasing in power by 1912. However, it gained even more power over the course of the century. This happened through crises such as wars and through the increasing power of the media. The judicial branch increased its power tremendously during this period. This happened largely during the 1960s as the Warren Court got the judicial branch more involved in a number of areas that it had not previously affected. In these ways, these two branches came to be more powerful relative to the legislative branch.