Final answer:
The legislative branch, specifically the U.S. Senate, must ratify treaties. While the President can negotiate treaties and issue executive agreements, the latter do not require Senate ratification unless they alter federal law or involve financial commitments restrained by Congress's power of the purse.
Step-by-step explanation:
The entity that often takes part in the treaty process and must ratify treaties is the legislative branch. In the United States, this means the U.S. Senate is responsible for giving its advice and consent to the treaty by a two-thirds vote, as outlined in Article II of the U.S. Constitution. The executive branch, through the President, has the power to negotiate treaties with foreign governments, but without Senate ratification, these treaties cannot become legally binding.
Presidents can also issue executive agreements with foreign powers, which do not require ratification by the Senate. However, the use of executive agreements over treaties, such as the Iran Nuclear Agreement, sometimes leads to debate. While executive agreements can be enacted without congressional action, they must not conflict with existing U.S. domestic laws.
The U.S. decides to participate in treaties and international organizations based on a variety of factors, including strategic interests, global stability, economic benefits, and to address international issues collaboratively. This decision-making process typically involves an assessment of the advantages and disadvantages of entering such agreements or organizations, and how they align with U.S. foreign policy objectives.