He was Interior Minister from December 1916 to January 1918, also under Brătianu. His term coincided with a critical period: Romania had joined the war in August; a German offensive from mid-November to early December had forced King Ferdinand and the government to flee to the temporary capital of Iași, in the Moldavia region. The loss of two-thirds of the national territory posed acute problems, including for Constantinescu's ministry. He ordered numerous law enforcement agencies to retreat to Moldavia, although the Romanian Police and part of the Gendarmerie stayed in place. Subsequently, he reorganized the law enforcement and intelligence command structure, while strengthening police presence in Moldavian cities and towns. He made efforts to strengthen intelligence-gathering through special security brigades in Roman, Tecuci, Piatra Neamț and Vaslui, among other cities. The gendarmes guarded sites of economic and military importance, lines of communication and the military engineers' work along the front. A new agency was formed to guard dignitaries and counter espionage against the Romanian Army, while a group of 160 gendarmes was put together to guard military sites in the Danube Delta. Each infantry division was assigned a police company for counterespionage purposes.