De Gregorio was a parliamentary assistant at the
European Parliament until 2004. In 2005, after the failure of an agreement with
Forza Italia, he ran for regional elections in Campania on the list of
Gianfranco Rotondi, the
Christian Democracy for Autonomies. In 2005,
Italians in the World became a political movement and reached an agreement with the
Italy of Values for the
2006 Italian general election. In April 2006, De Gregorio was elected to the Senate on the
Italy of Values (IdV) list. On 7 June, he was elected president of the Defence Commission thanks to an agreement with the
House of Freedoms reached directly with the mediation of the Senate group leader of Forza Italia,
Renato Schifani, in contrast to the candidate of
The Union, the ex-partisan
Lidia Menapace. The vote of De Gregorio himself, who by voting himself with the senators of the House of Freedoms had put in crisis the majority of The Union, was crucial. On 25 September 2006, after further controversy following his abstention during the vote of an indult order, De Gregorio announced his definitive exit from IdV and from the
centre-left coalition majority, subsequently voting against the
second Prodi government's confidence during the crisis of February 2007. In September 2007, De Gregorio officially returned to the
centre-right coalition, signing a federative pact between his movement and Forza Italia. On 24 January 2008, he voted for the
motion of no confidence against the Prodi government, contributing to its fall. In the
2008 Italian general election, De Gregorio was elected to the Senate of the Republic on
The People of Freedom list. Member of the Defence Commission and also president of the Italian Parliamentary Delegation to the Parliamentary Assembly of NATO, a post from which he self-suspended on 14 April 2012 in reference to the judicial proceeding that saw him investigated on the alleged misappropriation of €20 million of funding to the newspaper ''L'Avanti!'' == Judicial proceedings ==