The first and probably most significant indication that Mordini had come to see himself as a force for moderation came in August 1862, when he teamed up with fellow parliamentarians Nicola Fabrizi and , to make the trip to Sicily in order to dissuade Garibaldi from setting out on his ill-fated "liberation expedition" towards Rome. The intention, on the part of the passionately anti-papal Garibaldi, was to drive the pope from Rome, but Garibaldi and his men would be intercepted in Calabria, and never came close to Rome. Mordini failed to dissuade Garibaldi from setting out. Furthermore, he was himself suspected of being caught up in his charismatic former comrade's "mischief making". On 27 August 1862 Mordini and the other two members of his three man parliamentary delegation were arrested in Naples. The three of them were incarcerated in the Castel dell'Ovo for more than six weeks, released only in the context of a wider amnesty granted by the king to Garibaldi and his companions in respect of the failed "liberation expedition".