The term Constitutional arch (Italian: Arco costituzionale) was conceived and used in the Italian political debate during the first fifty years of the Italian Republic. This expression linked the Italian political parties which had been actors in the drafting and approval of the Italian Constitution of 1948.
The arch therefore included the Christian Democracy (DC), the Italian Communist Party (PCI), the Italian Socialist Party, the Italian Democratic Socialist Party, the Italian Liberal Party and the Italian Republican Party, then practically all major parties except the Monarchist National Party and, particularly, the Italian Social Movement (MSI), which had no Members of Parliament (MPs) in the Constituent Assembly and did not share the anti-fascist values contained in the Constitution itself.
According to Claudio Pavone the arch was the heir of the constitutional system of government led by the National Liberation Committee, maintaining the structure for a long time even after the ouster of the center-left government in 1947. The Constitutional arch was also one of the support points used as motivation, during the years of lead, from politicians who demanded a government of national unity including the PCI fully into the leadership of the country.
The Constitutional Assembly had the effect of creating an asymmetry between the forces of the left opposition (included within the Constitution) and of right opposition (not the same) than the governments of the so-called First Republic that until 1994 were based on DC. Indeed, the PCI, despite being at opposition permanently since 1947, was an active component of the policy making process, both nationally (especially during the parliamentary legislative committees) and in local administrative areas, such as governments of regions, provinces, while the MSI, more or less everywhere, was confined to the margins of political life.
One of the last acts of political expression in the constitutional election was the President of the Republic of Sandro Pertini, elected on July 8, 1978, receiving the largest majority in presidential vote in Italian history.
The theory of the constitutional arch, during the seventh parliamentary terms (1976–1979), was challenged by the Socialist Party, led by Bettino Craxi as his new secretary, who began to introduce political discourse in the demand for constitutional reforms, a hypothesis until that time always firmly rejected by any party of the arch, and was generally considered completed when Craxi, during which he held the office of Prime Minister of Italy, found in favor of a hypothetical chance for MSI to enter into a coalition government as a sign of relaxing at the party offered the chairmanship of the Board of elections to the Italian Chamber of Deputies.
- The first MSI's MPs were elected by the election of 1948, held after the constitutional approval.
- The Action Party, which had contributed the wording of the constitution, disbanded well before the political debate to formulate this expression.
- Claude Peacock, The legacy of civil war and the new institutional framework by P. Bevilacqua.