Why is the president the only person allowed to conduct measures of foreign policy?

Yes, the President is only one to who is allowed to conduct measures of fiscal policies.

The president is the only authorized person who is allowed to conduct foreign policies. He/she is having the supreme power in America. The president negotiates the treaties with the foreign countries. After that treaties comes into force only if is ratified by two third of the senate.

In USA, President is the commander in chief of US armed forces so it also has so many authorities over the armed forces. Ambassador and Secretary of state are appointed by the President along with the "Consent of the Senate".

the above statement/question is (true);

an informal structure in a bureaucracy would be something like so-called "office politics". where there's a formal structure set up for the organization, but then an informal subculture as well that has a way of organizing the bureaucracy further. this can be positive because it sets up an added degree of organization, albeit informal, within the bureaucracy.