The president has the power to negotiate treaties with foreign nations, but such agreements on behalf of the united states must be approved by

 A two-thirds majority of the US Senate.

Details:

Article II, Section 2 of the Constitution lays out the process for treaties made by the United States with other nations.  That section of the Constitution says of the President, "He shall have Power, by and with the Advice and Consent of the Senate, to make Treaties, provided two thirds of the Senators present concur."

The advice and consent of the Senate typically comes after the treaty has been negotiated by the President.  As reported by Justia (a legal information site), "The Senate’s role in relation to treaties is essentially legislative in character."  In a Supreme Court decision in 1936, this was affirmed by the Court's decision, which said, that the President "alone negotiates. Into the field of negotiation, the Senate cannot intrude" (United States v. Curtiss-Wright Export Corp., 1936).   However, for the treaty to become active, the President must secure approval by the Senate, with a two-thirds majority vote, as stipulated by the Constitution.

An article on the United States Senate's own webpage concerning "Advice and Consent of the Senate" notes that this provision in the Constitution was connected to the overall idea of separation of powers that the founding fathers had in mind.  In The Federalist Papers (#75, #76), urging ratification of the Constitution,  "Alexander Hamilton argued that the provision afforded a necessary means of checks and balances."

relations between the soviet union and the united states were driven by a complex interplay of ideological, political, and economic factors, which led to shifts between cautious cooperation and often bitter superpower rivalry over the years. the distinct differences in the political systems of the two countries often prevented them from reaching a mutual understanding on key policy issues and even, as in the case of the cuban missile crisis, brought them to the brink of war.

the united states government was initially hostile to the soviet leaders for taking russia out of world war i and was opposed to a state ideologically based on communism. although the united states embarked on a famine relief program in the soviet union in the early 1920s and american businessmen established commercial ties there during the period of the new economic policy (1921–29), the two countries did not establish diplomatic relations until 1933. by that time, the totalitarian nature of joseph stalin's regime presented an insurmountable obstacle to friendly relations with the west. although world war ii brought the two countries into alliance, based on the common aim of defeating nazi germany, the soviet union's aggressive, antidemocratic policy toward eastern europe had created tensions even before the war ended.