According to the constitution only the has the power to negotiate a treaty

According to the constitution only the PRESIDENT has the power to negotiate a treaty.
The president is considered to have a "first mover" advantage when involved in treaty making because Congress cannot initiate treaties and can only consider them once they have been negotiated by the president.
When a president claims that the president's discussions, decisions, and documents can be shielded from other branches of government, the president is claiming executive privilege.