Both Quill and O'Dwyer had been born in Ireland. Impelliteri was born in Sicily but came to the US as an infant. The election of O'Dwyer in 1945 marked the return of Irish-dominated Tammany Hall to the mayoralty after being defeated by La Guardia, who had split off the Jews and Italians from the Tammany coalition. With the help of the American Labor Party and the Mafia, O'Dwyer brought most ethnic New Yorkers back in the Tammany fold. He celebrated his election with the song "It's a Great Day For the Irish." His administration was marked by an antipathy to Protestant civic and religious organizations in the city.
O'Dwyer began his term with a reputation as a gang buster and devout Catholic- he had studied for the priesthood- but his administration became the target of state and federal probes over police corruption and mob influence. Questions remain as to what extent O'Dwyer was personally involved in the corruption but the old gang went to town when they got back in the seat of power and O'Dwyer did nothing to stop them. New York politicos convinced Truman to appoint O'Dwyer Ambassador to Mexico, where he would be safe from the investigating committees, and O'Dwyer gladly skipped town. He stayed in Mexico for 15 years. Impelliteri took over as mayor and, as the police department scandal deepened, dismissed most of O'Dwyer's appointees. Not surprisingly. although he was a Democrat, Tammany did not back Impelliteri in the special election, which he won as an independent with the slogan "unbought and unbossed." Tammany would defeat him in the next regular election with Robert F. Wagner after painting him as an incompetent. Tammany claimed that they had picked his name out of a city manual to give ethnic balance to the 1945 ticket.