Matt Glassman, who currently teaches in the Claremont McKenna College Washington Semester, wrote the following for the Congressional Research Service:

Congress’s role and operation in national politics is fundamentally shaped by the design and structure of the governing institution in the Constitution. One of the key principles of the
Constitution is separation of powers. The doctrine is rooted in a political philosophy that aims to keep power from consolidating in any single person or entity, and a key goal of the framers of the
Constitution was to establish a governing system that diffused and divided power. These objectives were achieved institutionally through the design of the Constitution. The legislative,
executive, and judicial branches of the government were assigned distinct and limited roles under the Constitution, and required to be comprised of different political actors. The constitutional
structure does not, however, insulate the branches from each other. While the design of the Constitution aims, through separation, to prevent the centralization of power, it also seeks the
same objective through diffusion. Thus, most powers granted under the Constitution are not unilateral for any one branch; instead they overlap.

The constitutional structure of separation of powers invites conflict between the branches, particularly between Congress and the President. The electoral structure of the federal
government provides not only separate bases of authority, but also different bases of authority for political actors, as well as different time horizons. Likewise, the assignment of powers under the
Constitution is not only overlapping, but also somewhat vague, creating inter-branch contests for power across many key functions of the government. Finally, numerous questions of authority are
not even addressed by the Constitution.

Although each branch has strong incentives to protect its prerogatives, in many cases individual political actors have incentives that run counter to their institutional affiliation. In particular,
political actors will often, quite reasonably, place the short-term achievement of substantive policy goals ahead of the long-term preservation of institutional power for their branch of
government. Likewise, partisan or ideological affiliations will at times place political actors at cross purposes, where they will be forced to choose between those affiliations and their branch
affiliation. Such anti-branch incentives are important contours to consider for political actors seeking to increase the power of their own branch.

The problem of institutional power coming into conflict with other goals is particularly acute for Congress, especially in relation to the executive branch. As individual members of a large body,
Representatives and Senators may not believe they have the responsibility or the capacity to defend the institution. Those who may feel such responsibility, such as party and chamber leaders,
will often find themselves in situations in which policy or party goals, either their own personal ones or those of their caucus, come into direct conflict with institutional goals. Even when
Congress does choose to institutionally defend itself, it often finds itself speaking with less than a unified voice, as only the most vital institutional powers have the ability to unify Congress.