Bush's presidency.He was nominated by Mr Bush to serve as US ambassador to the United Nations, but the strong supporter of the Iraq War was unable to win Senate confirmation. He resigned after serving 17 months through a recess appointment that allowed him to hold the job on a temporary basis without Senate approval.In 2018, Mr Bolton was appointed to serve as Mr Trump's third national security adviser His brief tenure was characterised by disputes with the president over North Korea, Iran and Ukraine.Those rifts ultimately led to Mr Bolton's departure, with Mr Trump announcing on social media in September 2019 that he had accepted his resignation.Mr Bolton subsequently criticised the US president's approach to foreign policy and government in his book, including by alleging that Mr Trump directly tied providing military aid to Ukraine to that country's willingness to conduct investigations into Joe Biden, who was soon to be Mr Trump's Democratic rival in the 2020 presidential election, and members of the Biden family.Mr Trump responded by slamming Mr Bolton as a "washed-up guy" and a "crazy" warmonger who would have led the country into "World War Six."AP