Who can secure treaties with foreign countries

The United States has tax treaties with a number of foreign countries. Under these treaties, residents (not necessarily citizens) of foreign countries are taxed at a reduced rate, or are exempt from U.S. taxes on certain items of income they receive from sources within the United States. These reduced rates and exemptions vary among countries and specific items of income. Under these same treaties, residents or citizens of the United States are taxed at a reduced rate, or are exempt from foreign taxes, on certain items of income they receive from sources within foreign countries. Most income tax treaties contain what is known as a "saving clause" which prevents a citizen or resident of the United States from using the provisions of a tax treaty in order to avoid taxation of U.S. source income.

The US President to propose and and chiefly negotiate agreements, but they must be confirmed by the senate.

Marshall plan is the answer.