THE I’s had been dotted; the T’s were crossed. The 55 delegates to America’s first and so-far-only constitutional convention had hammered out compromises on the separation of powers, apportionment of seats in the legislature and the future of the slave trade. But on September 15th 1787 George Mason, a plantation owner from Virginia, rose to his feet to object.

Article V of the draft text laid out two paths by which future amendments could be proposed. Congress could either propose them itself, or it could summon a convention of representatives from the states to propose them. Mason warned that if the federal government were to become oppressive, Congress would be unlikely to call a convention to correct matters. To protect the people’s freedom, he argued, convening power should instead be vested in the states. Should two-thirds of their legislatures call for a convention, Congress would have to accede to their demand: a convention they should have.

The constitution was signed two days later, with Article V changed as Mason had suggested. Since then 33 amendments have been proposed, with 27 subsequently ratified, a process which requires approval in three-quarters of the states (see chart 1). Whether the issue was great (abolishing slavery) or small (changing the date of presidential inaugurations), all 33 of the proposals came from Congress. Mason’s mechanism for change driven by state legislatures has never been used. Even politically informed Americans often have no idea it exists.

That could soon change. In recent years the Balanced Budget Amendment Task Force (BBATF)—a shoestring group that received just $43,000 in donations in 2015—has been campaigning with great success for such an “Article V” convention. There are now 27 states in which the legislatures have passed resolutions calling for a convention that would propose a balanced-budget amendment. The two-thirds-of-the-states threshold for calling a convention is 34. And, as it happens, there are seven states which have not yet called for a convention to propose a balanced-budget amendment, but in which Republicans control both houses of the legislature.

The earliest all seven could plausibly make the call is 2019, because Montana’s legislature is not in session again until then. Bill Fruth, a co-founder of the BBATF, says that by that point he hopes to have the other six in the bag. If he does, then a convention would be on the cards. If his efforts falter, a bigger push is waiting in the wings. Called the Convention of States (CoS), it promises amendments on three topics: a balanced budget, limiting the federal government’s power and establishing term limits for members of Congress. Led by Mark Meckler, a former Tea Party activist, the CoS got its first resolution passed in 2014. But it has grown fast. It is far better-funded than the BBATF and claims 2.2m volunteers across the country; its advisers include Jim DeMint and Tom Coburn, two influential former Republican senators. Its resolution has now passed in 12 states.

Mr Meckler, like Mr Fruth, says he aims to have 34 states signed up by the end of 2019. Outside observers take that prediction seriously. Pete Sepp of the National Taxpayers’ Union (NTU), which has long advocated a balanced-budget amendment, puts the probability of an Article V convention being called by 2020 at 50-50. So does Jay Riestenberg of Common Cause, an organisation devoted to government reform which fiercely opposes an Article V convention.

Take a bow for the new revolution

The idea has support that extends well beyond those fixated on fiscal probity. Although the most successful Article V campaigners have been conservatives, some on the left like the idea, too. They think the status quo is defective, that constitutional fixes need to be applied and that a convention ostensibly called for the purposes of a balanced-budget amendment might, once in session, be convinced to widen its ambit and consider other amendments too. This prospect—a “runaway” convention—persuades others that Article V is a Pandora’s Box which needs to be kept firmly shut. It may not be much longer before it becomes clear which side is right.

The want of any previous Article V convention in the past 228 years is not for lack of trying. No one has a firm count of the number of resolutions that state legislatures have passed calling for one, but it is over 500. In 1963 Arkansas even passed a resolution calling for an Article V convention to put forth an amendment removing Mason’s convention procedure from Article V. Today, 42 states have at least one Article V application pending.

Given that Article V says Congress must call a convention once two-thirds of the states have asked for one, why has it not? One answer is that no one with standing has gone to court and asked it to. Another may well be that, without conscious deliberation on the subject, Congress has decided that it needs 34 applications not just for any old convention, but for a specific convention: applications that share a topic, wording and the like. This is what the BBATF and CoS are trying to provide.

They are not the first to make such a push. In the 1970s the NTU began a campaign to pass state resolutions for a convention on a balanced-budget amendment. By 1983 the project was on the brink of success; 32 state legislatures, some of them Democratic, had signed up, and California and Montana were set to hold ballot initiatives that would have forced their legislatures to add to those applications. But state courts ruled the two ballot initiatives unconstitutional, and the effort stalled (see chart 2).

With the amenders’ momentum sapped, their opponents gained the upper hand. Somewhat surprisingly, the most effective response came from the right. The John Birch Society, a far-right fringe group, launched a counter-campaign; the Eagle Forum, a conservative group best known for its fight against an amendment guaranteeing women equal rights to men, led a similar charge. By the late years of Bill Clinton’s presidency the budget was in surplus, taking further wind out of the movement’s sails. Many states which had passed resolutions rescinded them. But under George W. Bush the deficit returned, and in 2009 the financial crisis drove it up to levels not seen since the second world war. “When I saw [the Federal Reserve] printing currency, that’s when I got motivated to work on this,” says Mr Fruth. “I became frightened as a citizen.” One year later, Republicans swept the midterm elections. Democrats lost hundreds of seats in state legislatures. Because 2010 was a census year the newly empowered Republicans were in a position to oversee redistricting, and thus in some places able to cement their new advantage. In 2009 there were 14 states where Republicans controlled the whole legislature. By 2017 there were 33. The landslide of 2010 opened a purely partisan path to a convention. Since 2010 the BBATF has helped get resolutions passed in 15 states which previously lacked them. But its opponents have swung back into action, too. They fall into two camps: those who fear that an Article V convention will do what its advocates want it to, and those who fear that it will not. The first cohort consists primarily of liberals, who see a balanced-budget amendment as a vehicle for right-wing dreams of rolling back America’s welfare state. “The right is very frustrated with Congress’s inability to cut these social-safety-net programmes, and this is their backdoor way to do it,” says Chris Taylor, a Democratic assemblywoman in Wisconsin. At a conference held in 2013 by the American Legislative Exchange Council, a group that writes model conservative bills for state lawmakers to introduce, Ms Taylor remembers hearing delegates talk about “the purpose being to kneecap the federal government and prohibit it from regulating and spending in every area except national defence.” A larger group of critics, whose strange bedfellows include the Birchers, the American Civil Liberties Union and Common Cause, has focused on the risk of a runaway convention veering off into non-budgetary topics. The opportunity to propose amendments without the normal hurdle of getting them past two-thirds majorities in both the House and Senate might prove hard for ideologues to resist. Would conservative delegates really vote against, say, a separate amendment asserting that the protections of citizenship start at conception?

Arguments like this have worked in some more liberal states. Delaware, which passed an application for a balanced-budget amendment in 1976, rescinded it last year; New Mexico, Maryland and Nevada followed suit in 2017. But that tactic seems to have run out of room; none of the remaining 27 states looks likely to rescind. Instead the focus is now on the seven states with Republican-controlled legislatures that have yet to request a convention: Idaho, Kentucky, Minnesota, Montana, South Carolina, Virginia and Wisconsin. In some of these states, opponents are putting up a strong enough fight that a convention is not a foregone conclusion. In March the Idaho Senate, where Republicans hold a 29-6 majority, shot down an Article V application.

Virginia’s House of Delegates approved an Article V application in 2016, but Richard Black, a Republican state senator, has helped stymie the resolution’s progress with warnings of devious Democrats hijacking a convention. “They could change freedom of religion to say certain teachings from the Bible are hate speech,” he told supporters by e-mail in 2015. “They could take away our right to own a gun.”

And there are indeed people on the left who like the idea of turning such a convention to their own ends. Two Republican majorities in Congress alongside a Republican president have made the idea of restraining the federal government more appealing to liberals. An Article V convention has a prominent advocate in Lawrence Lessig, an idealistic law professor at Harvard, who argues that it is the only way to achieve campaign-finance reform. Mr Lessig envisions a grand bargain of “electoral integrity for fiscal integrity”, in which the left would reduce the amount of money in elections and the right would reduce the amount spent by government.

To allay the fears that Mr Black and Mr Lessig might stir in Republican hearts, the BBATF and CoS insist that a convention could put forward amendments only on the subjects listed in the states’ applications. Sponsors in some states, such as Wisconsin, have proposed state laws that would ban delegates from casting votes on unrelated topics. But Article V itself says nothing about limiting the scope of a convention. Indeed, it says nothing about many issues which, were a convention to be called under its auspices, would become contested: who would attend; whether it would be open to states that had not called for it; what limits might be placed on its delegates; by what majority an amendment would need to pass to be proposed; and so on.

In the absence of such guidance the BBATF convened a meeting in Phoenix this September to hammer out its own rules for a convention. In spite of a raucous group of protesters—one dressed as George Washington, complete with wig and stockings, and another wielding a sign scolding the delegates “You’re No Hamilton”—they agreed to give each state one vote regardless of population, and to limit the subject matter to the issue named in the states’ resolutions, even if a supermajority wished to add new topics.

But fun as they were to debate, the recommendations from the pow-wow in Phoenix have no formal standing. Nor do the rules that passed the Senate Judiciary Committee in 1984 for the convention on the balanced-budget amendment then being proposed, which would have seen the senior senator of the majority party and the Speaker of the House preside over the convention, and required a three-fifths vote of delegates to establish rules of procedure. If Congress does call an Article V convention, it can also pass a new law governing the delegates’ behaviour.

But if the convention ignores such strictures, there might be no way to enforce them. Once a convention was under way, its procedures would almost certainly be immune to judicial review. In 1939, when the Supreme Court refused to set a ratification deadline for a proposed constitutional amendment, it established a precedent that the mechanics of amendments are a “political question”, reserved for elected branches of government. “There is absolutely no force that can override what the convention does,” says David Super, a professor at Georgetown Law. “Congress can send them rules, state legislatures can send them rules, but they can do what they want. I’m not sure there’d even be one vote for blocking it on the Supreme Court. The precedent is that strong.”

Liberated from the fold

The convention’s freedom applies only to proposing amendments. Those changes still need to be ratified by 38 states—which proponents of a convention say offers a crucial check on anyone doing anything they do not approve of. Mr Lessig dismisses CoS’s wish list of amendments as “a certain loser” at the ratification stage. Mr Meckler says Mr Lessig is “fantasising” about a campaign-finance amendment: “Political reality makes [it] unviable.”

But the logic of a convention might argue against such purity. The delegates, expecting the support of the solidly Republican state legislatures that had called the convention, would know they needed some split legislatures for ratification. Would they really be above crafting their amendment so as to contain something enticing to the other side?

There is also the possibility that Congress could choose ratification by means of state conventions. This is a constitutionally approved alternative to ratification by state legislatures, which has so far been used only once—for the amendment that repealed the prohibition of alcohol. In that case many states determined the make-up of their convention by a popular vote which in effect became a referendum on the amendment. As a balanced-budget amendment might, in some states, be more popular with the public than with legislators, it might be more easily ratified by this unusual route. Polls have consistently suggested that 65-70% of the public support such an amendment in principle.

There is also a long game to be played. The states do not have to ratify the amendment all at once, or in a rush. The 27th amendment, which prevents members of Congress from raising their salaries, was proposed in 1789; it did not get its 38th ratification until 1992. Unless the proposers put a time limit on their amendment’s ratification—as has been the case for most 20th-century amendments—it can sit around accumulating ratifications in perpetuity. As Mason intended, the federal government would have no way to block the process. Though some states might in time try to rescind their initial ratifications, this would be another area where the constitution is mum and the courts will not venture.

And then there is, as there always seems to be, a nuclear option. Delegates could simply declare a new, lower threshold for ratification. Uniquely in matters concerning Article V conventions, there is actually some precedent for this. The Articles of Confederation, signed in 1777 and ratified by all 13 original states in 1781, required the unanimous consent of all states for any changes. The constitutional convention of 1787 ignored this, deciding that ratification by nine of them would be sufficient for their document to replace the articles. Unless Article V is amended first, a convention would have no constitutional power to change the ratification rules itself. But delegates still might try. “The sovereign people have the right to alter or abolish their form of government and change it to whatever they want,” says Larry Greenley of the John Birch Society. “This is a convention that creates constitutions. It’s a level above state legislatures, and can’t be limited. We really believe that any Article V convention would have the ability to change the ratification process.”

A legal requirement to balance the budget could, if it included no safety valves, greatly damage the government’s ability to manage economic shocks. If it were carefully drafted, it might conceivably do a modicum of good. Whether that would be worth the risks of triggering an untested and remarkably poorly constrained constitutional mechanism with huge potential power, though, is another matter.

Correction (September 29th): An earlier version of this story said that the full Senate passed a bill in 1982 laying out rules for an Article V convention. In fact the bill only passed the Senate Judiciary Committee, in 1984.