What Is Brexit, and Why Can’t They Get It Done?

LONDON — After years of delays, stumbles and intermittent negotiations, Prime Minister Theresa May this week finally presented a draft plan for Britain’s withdrawal from the European Union — and it has been roundly and loudly panned. Her government may be verging on collapse.

Supporters of Brexit had promised that leaving the European bloc would be quick and simple. But it has turned out to be the opposite. To understand why, it helps to understand the origins and how that history is playing out today.

Britain joined the forerunner of the European Union in 1973, but British politicians have always been ambivalent about the bloc. The issue has long divided both of the country’s major parties, the Conservatives and Labour, and it became especially divisive among the Conservatives. In June 2016, Prime Minister David Cameron decided to settle the question with a yes-or-no national referendum.

Cameron bet that the country would not risk of leaving the European Union. He was wrong. Britons voted 52 percent to 48 percent to leave.

They then faced a predicament: The campaign to quit the bloc had promised to “take back control” from Europe but never explained how. Embittered Remainers who lost the vote accused the Leavers of lies and xenophobia.

May replaced Cameron and was charged with negotiating a Brexit deal with the European Union. Her biggest challenge was building support at home. One pro-Brexit faction has championed a clean break, so Britain would regain sovereignty over trade and immigration, while breaking free of the EU’s institutions, including its Court of Justice, a particular concern for them.

Others preferred to maintain close economic ties with the bloc, even if that meant sharing some control with the European Union.

With Britain scheduled to leave the EU on March 29, May has been trying to broker a compromise to avoid a chaotic “cliff edge” withdrawal that could leave ports blocked, airlines grounded, and food and drugs running short. That was the draft she presented Wednesday.

The Achilles’ heel of a Brexit deal is the border between Ireland, a member of the European Union, and Northern Ireland, part of the United Kingdom. For years, this border was militarized because of sectarian violence that left more than 3,500 people dead. But with the 1998 Good Friday peace accord, free trade was allowed.

This was possible because Ireland and the United Kingdom were members of the European Union. But when Britain voted to leave, the Irish border again became an issue. Reintroducing customs controls would pose many problems.

May’s draft agreement proposes keeping Northern Ireland, and the rest of the United Kingdom, in a European customs union until a trade plan that does not require checks at Ireland’s border is ready — so perhaps indefinitely. But this means Britain would also still be subject to some of the bloc’s trading rules and regulations.

In short, while paying a $50 billion divorce bill, Britain would remain bound by many EU rules without any say in the making of them. This infuriates the hard-line Brexit crowd, who say it would leave Britain as a “vassal state.”

They aren’t the only ones offended. The Democratic Unionist Party of Northern Ireland, which provides a crucial 10 seats to May’s minority government, is also furious, partly because the plan would impose more European rules on Northern Ireland than on the rest of the United Kingdom.

And don’t forget Scotland, which wants to remain in the European Union and is wondering why it cannot have the same deal as Northern Ireland.

No one really knows. If all goes well for May over the next few weeks — far from assured — then EU leaders will complete the deal at a summit meeting. It would then need the approval of the British and European Parliaments. The route to that outcome is treacherous.

May is fighting for her political life amid a big Brexit backlash in Parliament and calls within her Conservative Party for a no-confidence vote. Few experts think the British Parliament will approve her plan.

The opposition Labour Party has made clear its lawmakers will vote against, hoping to secure a general election. The Scottish National Party and the centrist Liberal Democrats are likely to do the same.

On Thursday it became clear that even Conservatives who campaigned to remain in the European Union were planning to vote against the draft agreement, hoping that the resulting crisis could mean a softer Brexit, or no Brexit.

If the plan were rejected, Parliament could ask the prime minister — or her successor, if she should step down — to negotiate another deal, although the European Union is highly unlikely to agree. And time is running out before the March 29 deadline.

There could be a general election, or Britain could face the cliff edge departure so feared by business.

There is even talk that the oft-heard pleas for a second referendum on Brexit might finally gain traction.