I believe I interpret the will of the Congress and of the people when I assert that we will not only defend ourselves to the uttermost

What is the main purpose of mentioning the will of the Congress and of the people here?

A. To assert the right to make a decision without input from others.

B. To deflect responsibility for the decision to go to war.

C. To maintain a diplomatic tone with the allies.

D. To put forth a united opposition to the attacks.