Renzi publicly challenged Letta for the position of Prime Minister on 13 February 2014. Letta quickly lost the support of his colleagues and resigned as Prime Minister on 22 February. Following his resignation, Letta initially retired from politics, leaving Italy to accept appointment as dean of the School of International Affairs at Sciences Po in Paris. In March 2021, the PD secretary Nicola Zingaretti resigned after growing tensions within the party. Many prominent members of the party asked Letta to become the new leader; after a few days, Letta announced that he would return to Italy to accept the candidacy, and he was elected as new secretary by the national assembly on 14 March 2021. On 4 October 2021, Letta was elected to the Chamber of Deputies for the Siena district. Early life and education Letta was born in Pisa, Tuscany, to Giorgio Letta, an Abruzzo-born professor of mathematics who taught probability theory at the University of Pisa, member of the Lincean Academy and of the National Academy of the Sciences, and Anna Banchi, born in Sassari and raised in Porto Torres of Tuscan and Sardinian origins. Born into a numerous family, uncles on his father's side include the centre-right politician Gianni Letta, a close advisor of Silvio Berlusconi, and the archeologist Cesare Letta, while one of his paternal aunts, Maria Teresa Letta, served as vice president of the Italian Red Cross; a maternal great-uncle is the poet and playwright Gian Paolo Bazzoni. After spending part of his childhood in Strasbourg, Letta completed his schooling in Italy at the liceo classico Galileo Galilei in Pisa. He has a degree in political science, which he received from the University of Pisa and subsequently obtained a PhD at the Sant'Anna School of Advanced Studies, a Graduate School with university status. From 2001 to 2003, Letta was professor at the University Carlo Cattaneo near Varese, and then he taught at the Sant'Anna School in Pisa in 2003 and at the HEC Paris in 2004. Political career Letta, a catholic, began his political career in the Christian Democracy (DC), the dominant centrist and Roman Catholic party, which ruled Italy for almost fifty years. From 1991 to 1995, Letta was president of the Youth of the European People's Party, the official youth wing of the European People's Party, a political party at European level founded by national-level Christian democratic parties, including the Italian DC; he