> 3. The parliament (for the US the Senate) ratifies the treaty, making it binding.
Under international law, ratification happens when a state’s international representatives (head of state, ministers, ambassadors) formally lodge instruments of ratification with the depositary. (See Article 2(1)(b), Vienna Convention on the Law of Treaties.) When the US Senate "ratifies" a treaty, that is not ratification under international law, that is a domestic legislative procedure which confusingly happens to have the same name.
Under international law, legislatures are not involved in ratification, only the state's international representatives are (which almost universally belong to its executive). Domestic law may require those representatives to consult or seek approval from the legislature, but international law mostly (but not entirely) doesn't care about those requirements.
Under international law, ratification happens when a state’s international representatives (head of state, ministers, ambassadors) formally lodge instruments of ratification with the depositary. (See Article 2(1)(b), Vienna Convention on the Law of Treaties.) When the US Senate "ratifies" a treaty, that is not ratification under international law, that is a domestic legislative procedure which confusingly happens to have the same name.
Under international law, legislatures are not involved in ratification, only the state's international representatives are (which almost universally belong to its executive). Domestic law may require those representatives to consult or seek approval from the legislature, but international law mostly (but not entirely) doesn't care about those requirements.