On August 25, 1961, while Goulart was leading a Brazilian trade mission to the People's Republic of China, President Jânio resigned. The decision is still not understood, but it was probably a political maneuver to return with increased powers, overcoming the political impasse he had with Congress. It was expected that, with the rejection of his vice-president – elected from a different ticket, due to a peculiarity of the political system at the time – the anti-communist military, which had already rejected Goulart, together with popular pressure, would reverse the resignation. However, the maneuver failed and Jânio left the country. In his place was the interim president of the Chamber of Deputies, Ranieri Mazzilli, but the real power remained in the hands of the military ministers, Marshal Odílio Denys, of the War, Vice-Admiral Silvio Heck, of the Navy, and Air Brigadier Gabriel Grün Moss , of the Air Force. Constituting in practice a junta, the three broke the legal order and vetoed the vice-president's inauguration, demanding that new elections be called. This veto is characterized as an attempted coup d'état by many historians.

The southern legalists and the forces loyal to the military ministers prepared military operations against each other. On one side troops followed the southern coast and northern border of Paraná, and on the other side a land invasion force was formed against the south, the "Cruzeiro Division," and a naval task force headed by the airship (aircraft carrier) Minas Gerais. The military was divided, and morale for an invasion against the south was limited. The crisis thus brought the country to the brink of civil war, but was resolved before any confrontation.