Joshua B. answered 03/06/21
Knowledgeable, Versatile, and Observant UNH History Tutor
D. None
The importance of a President's ability to be first mover is important primarily for things such as foreign policy (especially treaties), since Congress cannot negotiate treaties, but simply approve or reject treaties that have been negotiated already.
As for most foreign policy questions, Congress is arguably to large and too concerned with the country as a whole for the entire body to be conducting foreign policy directly. Therefore, the Executive branch, within limits, conducts most of the management of foreign policy questions on a daily basis.