This week, following Donald Trump’s state visit, Theresa May will officially resign as British prime minister, and the contest to find her successor as Conservative Party leader will formally commence. The vacancy at 10 Downing Street occurs less than three years after May, who succeeded fellow Tory David Cameron, pledged to implement the Brexit referendum to quit the European Union. Yet she leaves office with Britain still a member. Two deadlines for shedding EU membership have passed, with a third attempt set for the end of October.

One of the delays forced the U.K. to hold elections for the European Parliament, a legal requirement of EU membership. The Conservative Party lost almost all its seats, but the electoral results proved rewarding for a new political force—Nigel Farage’s Brexit Party, which made a simple appeal: get out now.

The Labour Party managed to lose much of its vote, too. Presiding over a coalition of working-class Leave supporters and a larger group of Remainers, Labour seemed unable to make up its mind. The Liberal Democrats, meantime, surged, as voters who never made their peace with Brexit sought a way to stop it. Once a small center-left party, the Liberal Democrats also offered a simple message: let’s have another referendum and stop the whole thing.

So why has Brexit proved so complicated? Why hasn’t Britain left yet? The 2016 referendum may have split Britain in two, but when divided, one side usually has a majority. Today, Britain is split in four.

The first group are the Dealers, who accept the Brexit referendum as a clear mandate for Britain to leave. Even most Conservative Remainers acknowledge that a democracy requires adherence to this vote. But Dealers also agree that the separation requires a withdrawal agreement with the EU—a settlement of outstanding debts, clarification on the status of citizens abroad, the establishment of a transition period, and a future trading bill to protect Britain’s economy. But there is a problem. The EU insists that any deal guarantee an open border between Northern Ireland and the Republican of Ireland. Known as the “backstop,” this provision would require a significant alignment between U.K. and EU interests on trade and regulation.

Then there are the No Dealers, perhaps 100 or so Tory MPs, who will vote against the Leave legislation if the backstop is included. The Democratic Unionist Party, whose 10 MPs are required for the government to maintain its majority, share this position. May failed to secure their support, which forced another delay, though they would have voted accordingly if she skipped an EU settlement. No Dealers acknowledge that leaving without a transition period will be tough, but they don’t share the Dealers’ fear of disaster. They hope to trade with the EU on terms similar to the World Trade Organization—but that would require an end to the backstop.

Though a minority among Tories in Parliament, No Dealers enjoy popularity with Tory members and voters. Most Leave voters still believe that the question is straightforward and democratic: we voted to leave, so we must leave. The idea of a deal seems like procrastination. The argument that it is the No Dealer MPs who blocked leaving, by voting down the deal, has not proved persuasive.

Two more groups muddy things further. The Different Dealers are those who want the withdrawal agreement attached to a declaration that Britain will negotiate a close relationship with the EU, aping its policies. This is Labour’s position, and while it has few true adherents, it has allowed the party to acknowledge the referendum result while not actually voting to support the deal required to leave. If Labour voted to leave, it would have infuriated the majority of the fourth group—the No Brexiters. This group seeks a second referendum, with Remain as one of the options, without being too picky about what the other option is (no deal, the deal, a different deal).

None of these groups commands a majority. An attempt to compromise between the Dealers and Different Dealers broke down, with Labour unwilling to commit to any different deal.

What will happen? No Dealers will likely win the battle on the right, as a new leader commits to leaving soon, even if Britain proceeds without a deal. The leadership probably can’t be won without some sort of tough stance. And the No Brexiters will win on the left, as Labour bows to demands for a second referendum. Which of these two prevails is harder to guess. It may need an election to settle it—but the Tories know that if they hold an election before delivering Brexit, the party may never recover.

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