On 24 September, Ardern became the first female head of government to attend the United Nations General Assembly meeting with her infant present. Her address to the General Assembly on 27 September praised the United Nations for its multilateralism, expressed support for the world's youth, and called for immediate attention to the effects and causes of climate change, for the equality of women, and for kindness as the basis for action.
After the whistleblower complaint became known in September 2019, House speaker Nancy Pelosi initiated a formal impeachment inquiry on September 24. The Trump administration subsequently released a memorandum of the July 25 phone call, confirming that after Zelensky mentioned purchasing American anti-tank missiles, Trump asked Zelensky to investigate and to discuss these matters with Trump's personal attorney Rudy Giuliani and Attorney General William Barr. According to the testimony of multiple administration officials and former officials, the events were part of a broader effort to further Trump's personal interests by giving him an advantage in the upcoming presidential election.