In The March of Folly, the eminent historian Barbara Tuchman offered three criteria for inclusion in the list of history’s most senseless decisions: when those who were responsible were warned in advance of the potential for disaster of what they were getting themselves into; when groups, not individuals, perpetrated the foolishness; and when there were feasible alternatives to the course they took.

With the official date of Brexit set, the people and leaders of the United Kingdom are on the brink of adding themselves to this dubious pantheon, and in so doing meet all three of Tuchman’s criteria. However, after nearly a million Britons marched last month  in favor of a second referendum, and with public polls in the United Kingdom continuing to swing against Brexit, there is realistic talk of a scenario in which British citizens may get another choice as to whether they wish to remain in the European Union.

In fact, in light of the fraught negotiations of Prime Minister May’s government with the European Union, with her cabinet, and with pro- and anti-Brexit Conservative members of Parliament, it is just as likely that the UK will crash out of the EU with no negotiated deal between them as it is that they will reach a deal that May can get through parliament—and just as likely that the British public will get a second chance to vote in a referendum under conditions of a more informed electorate. The United Kingdom has gone from being in the European Union and wanting opt-outs to being nearly out and wanting opt-ins.

In spite of this, the EU clearly would prefer the UK to remain, for a range of reasons: The UK has formidable defense, intelligence, and diplomatic capabilities, and Europe has made history together over many decades, creating a single economic market, borderless travel, and the unifying legal jurisprudence of the European Court of Justice (ECJ), as well as making all European citizens better off and acting as a beacon for the democracies of East Central Europe after the shroud of the Soviet Union was lifted.

It would be calamitous for both the United Kingdom and the European Union for Brexit to go forward. The EU would lose one of its most powerful and capable member states, and—as a vast range of high-minded studies have indicated—the UK will be much worse off, primarily in macroeconomic and personal livelihood terms. The UK would not even be able to rapidly negotiate a series of new bilateral trade deals with the United States and other countries, for other governments will be waiting to see what the specific nature of the UK’s trade relationship with the EU turns out to be, something that will not begin to be negotiated until the UK leaves.

But well ahead of that, there also happens to be plenty of irony and tragedy in the endgame of the Brexit negotiation itself. The departure deal is 95 percent complete, but the last 5 percent is proving dramatically difficult to finalize. The primary remaining areas of disagreement involve both the need to avoid a new hard border between Ireland and Northern Ireland, and whether the UK will remain partly or wholly in the EU Customs Union.

The European Union and its chief negotiator Michel Barnier have a difficult decision to make on its endgame negotiating strategy. They must decide whether to proceed to agree a final deal with the UK (and likely arrive at a “soft” UK exit), or refuse to agree on a final deal, in effect sabotaging May (and likely arrive at a possibility of a second referendum). The irony is that by sorting out the Irish border issue and getting to a final deal, the EU would be helping bring about an outcome it does not want.

The tragedy is that the best shot at keeping the UK in the EU would undermine May and probably force her from office. For in all likelihood, if the European Union were to exit without a deal, it would engender acute political instability in Britain, including a range of possibilities, such as May losing a confidence vote, pro-Brexiteer Boris Johnson replacing her, a fresh national election (that the Labour Party would likely win), and either May herself (before she bows out) or new Prime Minister Jeremy Corbyn calling for a fresh referendum.

Tragically, the set of conditions necessary for triggering a new referendum (that nearly all observers assume will lead to a majority vote for the UK to remain in the EU) will not necessarily be sufficient; the scenario of the UK failing to get a departure deal will be highly uncertain. May could easily lose her premiership to Boris Johnson, who most certainly would not lead the UK back in the EU once it got out. It is not precisely clear whether May could manage to get a vote in Parliament passed in favor of a new referendum, before she loses a no confidence vote, a party leadership vote, or both.

But as the costs mount and UK public opinion continues to shift in favor of remaining in the EU, the time has come for courageous leadership on both sides of the Atlantic to help the UK avoid the ultimate self-inflicted wound and save the vaunted special relationship. The Prime Minister is living politically on borrowed time, with the sparing grace of history to end up on her side only if she seizes the moment and defies expectations by keeping the UK in Europe—and America can help, though not in the Trumpian way one might presume.

First, British leaders and citizens alike have had ample warning of Brexit’s disastrous impact on the country’s economy and political standing. Moreover, the damage from Brexit will ripple beyond the British Isles: to the Continent, where it will amount to an enduring challenge to the permanence of the European Union; to Moscow, Beijing, and autocrats everywhere, who will see Brexit as proof of the vitiation of the liberal democratic order; and to Washington, where its long vaunted special relationship with a now less-significant, serially broken UK will undergo a substantial downgrading.

Second, though it has had prominent champions, including vocal Trump supporter Nigel Farage, Brexit remains largely an expression of group ‘id’ – a dark, damn-the-facts mix of anti-immigration, anti-Brussels, and anti-anything-that-smacks-of-elitist sentiments.  Neither Theresa May nor Jeremy Corbyn are politically or ideologically wedded to Brexit. Yet there simply is no truly significant political figure in the UK whose political destiny rests on Britain’s departure from the EU, not even Boris Johnson.

Third, and most important, the UK ship of state can actually avert the approaching Brexit iceberg. Unlike Tuchman’s examples of historical follies, the United Kingdom’s fate is wholly in its own hands, unaffected by the military or political stratagems of others. The only question is how to awaken Britain’s leaders and the wider public to seize this last opportunity to avoid the ignominy of a catastrophic self-inflicted wound. Tony Blair has tried to sound the alarm but remains too tainted by his Iraq debacle to command attention. Others, like Lord Kerr, the author of Article 50—the very provision that allows a country to exit the European Union—find their desperate urgings to turn back from Brexit mostly ignored.

Bereft of a Churchillian figure who can, in the great leader’s infamous words, “give the nation a roar,” it is the British people who need to show their leaders they still have a lion-like heart. As in the United States after the election of Donald Trump, ordinary British citizens will have to summon the will to resist the Brexit disaster. “Indivisible,” the post-Inaugural Woman’s March in Washington, and the widespread response to the violence in Charlottesville show that organizers can translate revulsion into mass action.

Converting grievance into action, however, will take more than a grassroots British movement. Theresa May has distinguished herself by a remarkable lack of leadership qualities. Her woeful performances at recent Conservative Party conferences have become the stuff of parody. She called an election and promptly lost her party’s parliamentary majority. She “commands” a Northern Irish party-supported thin margin in Parliament where her most important ally seems at times to be opposition leader Corbyn, whose potential ascent to 10 Downing Street inspires widespread anxiety in its own right.

May’s palpable weakness creates an opportunity for those with strength—chiefly France’s Emmanuel Macron—to craft a Remain deal with his counterparts in Brussels. But with his primary partner Angela Merkel now so weakened she won’t be running in Germany’s next election, even with strong support from the Dutch and Spanish Prime Ministers for a new deal more attractive to the UK in immigration terms, winning over Britain’s recalcitrant Brexiteers may not be in the cards. Negotiating as a united European Union to force the UK out without an exit deal may be their best shot.

At first glance, there appears little that the United States could do to prevent Brexit. President Obama, even with his high popularity in Britain, was unable to move the needle for the Remain campaign. And President Trump, loathed by many British, happens to be a toxic Brexit booster. Trump’s stance opens the door for the five living ex-Presidents—each of whom has now publicly criticized the current occupant of the White House—to speak out against Brexit.

A short, powerful joint statement in support of a second referendum issued jointly by Obama, Bush 43, Clinton, Bush 41, and Carter may well resonate across the Atlantic, and across the English channel. Ordinary Brits and officials alike would perhaps sit up and pay attention to remonstrations from “beyond the pond.” The joint missive would likely vex Trump into a pugnacious Tweet, only reinforcing the appeal of five former POTUS.

There is little doubt about the degree that the special relationship has already been hollowed out. May and Trump—in each leader’s feeble attempt to take their respective country down the wrong path—have reinforced the initial negative tendency of the other, thereby making Brexit and the U.S. retreat from global leadership more likely. May needs a post-Brexit trade deal with Washington; Trump needs political legitimacy from London. The conference of both have only served to hollow out the special relationship still further.

Trump aside, for its own interests the United States needs the UK to remain in the EU. More importantly, by any measure conceivable, it is in the UK’s own interest to cancel Brexit. Doing so is not difficult; it merely requires some timely application of vintage British pluck. Beyond the issue of how the referendum was not legally binding—and how Russian interference may well have tipped the vote—is the legal simplicity of a simple majority parliamentary vote to un-invoke Article 50, as Lord Kerr has pointed out. If the British government doesn’t do it, tragically the European Union may have to undermine Prime Minister May in order for the British people to have a second chance to safeguard their destiny.

Brexit is reversible. The dramatic damage to the world’s oldest democracy would not be, assuming that languid UK leadership persists in its quixotic gambit. If the British people ever wondered just how much their country matters, long after the demise of the British empire, now they know: a great deal indeed.