In 1933, Bonnet was a prominent member of the French delegation to the London Conference, where he was a leading critic of President Franklin D. Roosevelt's actions during the conference. In 1936, Bonnet emerged as the leader of 18 Radical deputies who objected to their party's participation in the "Front Populaire". As a result, the French Premier Léon Blum effectively exiled Bonnet in January 1937 by appointing him Ambassador to the United States, even though Bonnet did not speak English. Upon hearing of Bonnet's appointment, the American Ambassador to France, William Christian Bullitt, Jr. wrote to President Franklin D. Roosevelt about Bonnet: I don't think you'll like him. He is extremely intelligent and competent on economic and financial matters, but he's not a man of character. You may remember that he led the French delegation to the London economic conference where he led the attacks against you. Despite his short stay in the United States and his inability to speak English, Bonnet thereafter and for the rest of his life claimed to be an expert on all things American.