Despite thousands of attempts, the Constitution has been amended only 27 times in 225 years. Two of those amendments dealt with the same topic: Prohibition. The 18th Amendment started it. And 78 years ago this week, the 21st Amendment ended it.

The 18th Amendment illustrates the appeal — and pitfalls — of trying to use the amendment process as an easy way to eliminate a distasteful policy or practice. Amending the Constitution is not supposed to be easy. Its difficult by design.

To assure an amendment reflects national consensus, Article V of the Constitution erects two high hurdles in the amendment process. First, two-thirds of both houses of Congress — or two-thirds of the delegates at an amendment convention — must propose an amendment. Then, three-fourths of state legislatures or the states’ ratifying conventions must ratify it.

The 18th Amendment passed these hurdles but was hardly the model of careful deliberation. Congress conducted no committee hearings on it and spent only six hours in debate before approving it. The states ratified it within a month. This short-circuiting of the process would have lasting consequences.

The then-relatively new Progressive movement helped speed things along. Rejecting the Founders’ view that the purpose of government was limited to securing individual rights, Progressives argued that government should step in to solve social problems by regulating the economy, redistributing wealth and overseeing civil society.

In their view, the 18th Amendment was a national solution for a national problem: the violence and poverty associated with drunkenness. In reality, the alcohol-related poverty, violence and family deterioration were local problems that required local solutions.

Ultimately, this experiment in social reform failed because it sought to constitutionalize a particular policy preference. Many state officials didnt see alcohol as a national problem and, so, were reluctant to enforce prohibition. And, as organized criminals took over the alcohol business, they brought a new host of problems beyond drunkenness, violence and poverty. Ultimately, the Great Depression led to a drop in income-tax revenues, leading even the federal government to long for the steady stream of liquor-tax revenues. Together, these factors produced enough support to ratify the 21st Amendment and end Prohibition.

Our Constitution was written to establish a structure of government and to delineate certain processes for governance. It is not a list of policy prescriptions from the 18th, 19th and 20th centuries. Nor is it a mechanism to preserve transitory policy preferences. This is why, for example, the Constitution requires indirect taxes to be uniform, but it does not specify the rates for the taxation. The tax rate is a particular policy prescription that should remain the prerogative of the legislative process.

Structural amendments are meant to settle national questions of power — not local or temporary policy questions. Thus, the 12th Amendment (1804) changed the selection process for the president and vice president; the 20th Amendment (1933) truncated the period of time between a presidential election and the inauguration of the new president and addressed presidential succession; the 23rd Amendment (1961) gave the District of Columbia electors in the Electoral College.

Even the Bill of Rights focuses on structural limitations. The First Amendment clarifies the limits on Congress pertaining to the peoples fundamental rights of free exercise of religion, freedom of speech, of assembly, of the press and of petitions. The Ninth Amendment explains that the Constitution is not a list of rights, underscoring the 10th Amendments clarification that powers not delegated in the Constitution are reserved to the people and the states.

At key moments, the amendment process expands our constitutional discourse beyond the courts and political institutions to engage the American people in national conversation about fundamental questions. But our Constitution exists to allocate powers. Successful amendments address structural or procedural questions of governance, not policy prescriptions, no matter how commendable the motives of those backing the policies.

Julia Shaw is the research associate and program manager at the Heritage Foundation’s B. Kenneth Simon Center for Principles and Politics.