THE LAST time the United States held a constitutional convention was in 1787. That one turned out pretty well. The next one could have far more doleful results. And the nation is much closer to convening such a convention than many people realize.

It would take the votes of 34 state legislatures to call a constitutional convention to order. A majority of legislatures already have voted to do so. Such calls remain valid indefinitely — until 34 states have joined in a particular cause or the states rescind their appeals. Therefore we congratulate Maryland’s House of Delegates, which on Tuesday rescinded its call for a federal constitutional convention decades after approving it. Same to Nevada’s Senate, which voted, also Tuesday, to rescind a resolution in that state. But a number of states have recently passed or are close to passing measures calling for a convention.

The possibility was mostly dormant from the 1980s until a few years ago, when some blue states began calling for a convention to undo the Supreme Court’s Citizens United ruling and conservative groups began pressing red-state legislatures to pass convention resolutions on a variety of pet causes, including a balanced-budget amendment. Though each state might have a single issue in mind, once a convention is convened its delegates would not be bound to any particular issue. Gun control could be banned entirely — or its constitutional limits loosened; gay marriage could be eliminated — or the Equal Rights Amendment could be passed. Though it seems unlikely that the required three- fourths of states would subsequently approve major changes drawn up at a runaway convention, it is already amazing that so many states have taken the initial step of calling for one.

It is not even certain that three-fourths of the states would have to approve the convention’s work for it to become the law of the land, as the Constitution currently prescribes. The 1787 constitutional convention ditched preexisting ratification rules; who is to say a 2018 convention could not? In fact, nearly everything about this powerful process would be uncertain. Convention rules, which would be written ad hoc, could be manipulated to favor one party, region or interest group over another. Minority protections, so central to the Constitution’s guarantees, could be trampled upon. Sparsely populated states could impose their will on the majority of Americans who live in densely populated ones.

Many of us can point to one constitutional provision or another that we believe we could improve upon if given a chance. But a convention could do great damage to a charter that, on balance, has worked pretty well for a pretty long time. To take such a risk on behalf of a stupendously unworthy cause such as a balanced-budget amendment would be foolhardy in the extreme.