National security responsibilities fall across many entities in the federal government. which department, agency or bureau has the most influence and why

United States Department of Homeland Security

Explanation:

DHS is a cabinet department of the U.S. federal government. It was created in response to the September 11 attacks and it is the youngest cabinet department.

It is the third largest department, right after the departments of Defense and Veteran Affairs and it has the biggest budget of all the departments and the largest number of employees (240,000).

The mission of this department is to secure the nation from various threats, internally and externally, especially terrorism.

The DHS took over 22 previous federal departments which gave it an unique power, it is the department with the most far-reaching powers and privileges necessary to accomplish its goals.