America as a county does not have nuclear ambitions, we already have nuclear weapons and delivery mechanisms.
The phrase nuclear ambitions refers to a country that does not have nuclear weapons and a way to deliver them but want to obtain them, hence ambition.
If you are against nuclear proliferation, you want countries to stop developing and creating nuclear weapons.
Iran is used in this case as a foil for North Korea as they are both signors to the Treaty on the Non-Proliferation of Nuclear Weapons; Iran(1970), North Korea(1985).
Both countries have continued to work to develop nuclear weapons, with North Korea having conducted successful nuclear tests.
America fits the bill as a country with nuclear ambitions, and has done plenty of unfavourable trade shenanigans that said politicians have let slide