[5] A major factor in this move was pressure from the landowners to remove a threat to the system (notably, Constantin Garoflid filed a complaint with the king,[5] while Mihalache caused scandal when he publicly assured peasants that the monarch's opposition was ultimately irrelevant.

Mihalache became vice-president of the National Peasants' Party (PNȚ) in 1926, when the PNR and PȚ groups decided to unite in order to combat the effective monopoly the PNL had ensured after the voting of the 1923 Constitution.

[8] However, in 1928, Mihalache's voiced the party's call for a march on Bucharest, meant to topple Vintilă Brătianu's PNL cabinet: in May, large crowds gathered in Alba Iulia — despite the initial success in rallying all forces opposed to the National Liberals, the PNȚ did not capitalize on the gains, and continued instead to block activity in parliament.

The relations between the PNȚ and the monarch soured, however, especially after Vaida-Voevod's second cabinet fell in 1932, due to disagreement over several policies — as Minister of the Interior, Mihalache was directly involved in the dispute, as the scandal erupted when Gavrilă Marinescu, the prefect of police in Bucharest, refused to hand in his resignation, and instead called for the king's verdict.

[13] After 1938, when, faced with the rise of the Iron Guard, Carol imposed his authoritarian regime, the PNȚ party refused collaboration and merger into the National Renaissance Front.

According to the leading party member Ioan Hudiță, Mihalache, together with Virgil Madgearu and Mihai Popovici, continued to display support for the king and even considered joining the Front.

[15] Attacks and threats towards Mihalache in the Guard's press became widespread, and Mille Lefter singled him out as a former persecutor of the movement in a conference aired on Romanian Radio.

[17] He did, however, support the recovery of Bessarabia from the Soviet Union during Operation Barbarossa, and offered his services as a volunteer in the Romanian Army (June 1941) — he served for only a few days, and was discharged on orders from Antonescu himself.

[18] He eventually joined a semi-clandestine opposition, and then supported the PNȚ's entry into the underground liberation movement, as well as King Michael's pro-Allied August 1944 coup.

[22] The Communist regime which was installed in late 1947 outlawed the PNȚ altogether, alleging that Mihalache and Maniu had been trying to flee the country from the airfield in Tămădău, and had planned to give Romania a capitalist government-in-exile.

[23] Their capture on July 14, 1947 (see Tămădău Affair) and trial by a kangaroo court led to sentencing on November 11 to life imprisonment with requirements of penal labour.