The President of the United States of America is the Commander in Chief of all the branches of military of the United States, according to the clause 1 of article 2, section 2 of the constitution of the U.S.
The President, being the Commander in chief of all forces, has the full authority to give commands to all the military generals and to decide the use of the troops, weapons, ships, etc.
A political party is an organized group of people who have the same ideology or same political positions. And in an attempt to get them elected and thereby implement their agenda.