The senate has to ratify any treaties in order for them to become law.
That said, nothing prevents anyone from making bad decisions other than the other groups of people that must also be included in the decision. In theory, forcing Congress to ratify treaties prevents the President from doing something enormously stupid on his own accord, but it's certainly possible for a bad treaty to get past both branches of government.
Under Article II of the Constitution, the President is granted the power to deal with foreign affairs: this can be entering and discussing treaties, policy decisions, meetings with foreign heads of state, and executive agreements. However, treaties that the President enters into must be approved by Congress (2/3)--these are called congressional executive agreements, and they can be ex-ante or ex-post. Further, Congress can delegate certain elements of its own powers, such as law-making, if it is deemed to be closely connected with the President's goals of foreign policy.
executive agreements
Congress
Yes, the president can make foreign agreements through executive agreements. These agreements do not require Senate approval like treaties do, but they are still binding and carry the same legal weight as long as they fall within the president's constitutional authority.
Agreements that the president enters into that do not require the consent of the Senate are called executive agreements.
Executive Agreements!
Pacts between the president and heads of foreign governments are typically referred to as international agreements or treaties. These agreements can be formalized through diplomatic negotiations and may require approval by relevant governing bodies in each country.
The US Constitution divides the foreign policy powers between the President and Congress so both share in foreign policy.
State Department
He warned against foreign entanglement- agreements that could draw the US into foreign wars.
foreign policy
Executive Agreements