On the same day in 1946 that Winston Churchill delivered his Iron Curtain speech in the United States, Britain and the United States secretly signed the pact that formed the basis for their intelligence alliance. The partnership expanded during the advent of the Cold War to include other countries — Australia, Canada and New Zealand — earning it the name Five Eyes. All rely heavily on American intelligence to help keep their countries safe. Five Eyes officials have watched with alarm as Mr. Patel has fired agents who investigated President Trump and invoked his powers to investigate the president’s perceived enemies. The officials and others spoke on the condition of anonymity for fear of retribution.