The 26th Amendment to the Constitution took effect 50 years ago this summer, extending the right to vote to all Americans age 18 and older. It was the fourth amendment in the span of a decade, three of which expanded voting rights — a burst of democratic reform nearly unequaled in the nation’s history.

It was also the last meaningful change to the Constitution. And based on the country’s increasingly polarized politics, it is likely to remain the last for anyone alive today. (The 27th Amendment, ratified in 1992, was a historical quirk that doesn’t count for these purposes, as I explain below.)

This half-century drought is all the more distressing in a time of intense social and political turmoil, with demands from both the left and the right for large-scale reforms of the American system of government. Overturning the Supreme Court’s ruling in Citizens United, mandating a balanced budget, establishing a positive right to vote, banning the burning of the American flag? Forget it.

None of these frequently proposed amendments has anywhere near the level of support needed to clear the hurdles set out in the Constitution: a two-thirds vote in both the House and the Senate, followed by approval in at least three-quarters of the states, which today is 38. Sometimes even that isn’t enough. The Equal Rights Amendment, which would ban discrimination on the basis of sex, passed Congress in the early 1970s and picked up its 38th state last year. Yet it will probably never be adopted because it exceeded the time limit set out in the original bill and because several states that approved it later rescinded their ratification.

“We have an amendment process that’s the hardest in the world to enact,” said Aziz Rana, a professor of constitutional law at Cornell University. “That’s the reason why it’s basically a dead letter to enact constitutional amendments. You have to have rolling supermajorities across the country to do so.” Out of almost 12,000 amendments proposed since the founding, only 27 have been adopted. That’s one every 13.5 years on average, not counting the Bill of Rights, which was adopted as a package deal shortly after the Constitution was ratified.