This item represents one of the greatest sources of power for a president.
-strong popular support
-support of foreign countries
-political party affiliation
-military support

To answer the question above, they are all important, but in my personal answer is the strong popular support. without the popular support the movement of the president will not be as effective as to having the support of the many. It is also easier to manage if you are being supported by the many.

Strong popular support is the item among the items given in the question that represents one of the greatest sources of power for a president. The correct option among all the options that are given in the question is the first option. The president can implement his procedures once he or she is backed by a large popular support.

Internal combustion engines