Theresa May makes a statement outside 10 Downing Street on November 14.Henry Nicholls / Reuters

LONDON—With less than 140 days left before Britain leaves the European Union, negotiators have reached a provisional Brexit deal. The agreement, which was backed by U.K. Prime Minister Theresa May’s cabinet on Wednesday, marks a breakthrough in often fractious talks, and could offer businesses, officials, and private citizens a sorely needed road map on what life looks like for Britain outside the EU.

There is still one major hurdle for May to overcome, though: Will it pass muster with Parliament? No one—not least the prime minister herself—appears certain of the answer. And if it doesn’t, what was the point of her government rushing to get a deal past the finish line before it could guarantee political support?

The draft has already received widespread criticism from many of the lawmakers who could decide its fate in Parliament. From within May’s own Conservative Party, leading Brexiteers like Boris Johnson and Jacob Rees-Mogg have denounced the deal as “vassal-state stuff” and a “failure” that would see the U.K. beholden to European rules and regulations. At the opposite end of the party, the pro-Remain lawmaker Justine Greening told a rally calling for a second Brexit referendum Tuesday night that she would not support a deal that is “second best for this country.”

Sentiment is little different elsewhere in Parliament. In the opposition, Labour Party Leader Jeremy Corbyn criticized the government’s “shambolic handling” of the negotiations, noting that “this is unlikely to be a good deal for the country.” Scottish First Minister Nicola Sturgeon urged the government to reject a deal that “satisfies no-one and can’t command a majority” and return to the negotiating table instead. Arlene Foster, whose Democratic Unionist Party props up May’s governing majority in Westminster, signaled that her party would also vote down the deal.

Still, the government did have plenty of reasons for pushing to secure a deal (even if publicly, few say they will vote for it).

One reason is economic. Though negotiations with the EU could technically be drawn out until the new year, prolonging the process would force the government to step up its no-deal preparation and spending—a move that could spur additional economic uncertainty. “The longer we go with uncertainty,” Georgina Wright, a Brexit analyst at Chatham House, told me, “the more likely [that] businesses are going to kick in their contingency planning for no deal, because they need to ensure that they can continue to trade.”

Another reason is leverage. Up until this point of the negotiations, Britain’s politicians—both in and out of government—had been hopelessly divided. A deal, though unlikely to overcome those divisions, could give May an upper hand at home. “The mood, the context, the dynamics change once we have a deal,” Anand Menon, the director of the London-based U.K. in a Changing Europe think tank, told me. “Business will come out in support, the pound will rally, the Treasury will release forecasts that show” that this is a good deal, he added. “Things will look up all of a sudden,” he noted, “and that might put pressure on MPs.”

May needs at least 320 lawmakers to back her deal in a final vote for it to pass. Without a parliamentary majority or a unified party behind her, it’s estimated that May can only count on as many as 235 party loyalists, as well as four to five Labour lawmakers. Those who have already pledged to vote against her deal include a group of as many as 40 “hard-Brexit” Conservatives and a majority of Labour lawmakers, as well as the Scottish National Party (35 lawmakers), Liberal Democrats (12),the Welsh Plaid Cymru party (four), and the Greens (one).

The remaining number needed for May’s deal to pass must then come from other sources: Labour defectors, begrudging Tories who oppose May’s deal but prefer it to none, or Foster’s Democratic Unionist Party.

The deal has already overcome one major hurdle: the cabinet. After a more-than-five-hour meeting at Number 10 on Wednesday night, May announced that the deal received ministers’ collective backing. “This is a decisive step which enables us to move on and finalize the deal in the days ahead,” May said.

Though May appears to have avoided the high-profile cabinet resignations that have plagued these negotiations, a figure who could be key to the deal’s success in the days and weeks ahead is Brexit Secretary Dominic Raab, the prime minister’s pick to usher the deal through to its final phase after former Brexit Secretary David Davis’s resignation over the summer. A committed Brexiteer, Raab has been among the most vocal in the cabinet against a deal that risks keeping the U.K. closely aligned with the EU. If he is able to accept a provision to maintain some regulatory and customs alignment with the bloc to keep up the status quo at the Irish border, there is a chance others will too.

“If she doesn’t lose her Brexit secretary at this crucial moment, I think that will put her in a much more powerful position facing Parliament,” Henry Newman, the director of the London-based think tank Open Europe and a former adviser to Environment Secretary Michael Gove, told me. “She already lost one. To lose a second would be very careless and very difficult for her.”

“I believe that what I owe to this country is to take decisions that are in the national interest,” May said outside Number 10, “and I firmly believe, with my head and my heart, that this is a decision that is in the best interests of our entire United Kingdom.”

Ultimately, however, the fate of May’s plan won’t be decided by the cabinet, but by parliamentary calculus. The Conservative Brexiteer Peter Bone warned the prime minister in the House of Commons on Wednesday that if reports of the draft deal’s contents are true, the agreement could be dead on arrival. “You are not delivering the Brexit people voted for,” he said, “and today you will lose the support of many Conservative MPs and millions of voters across the country.”

If only a handful of lawmakers agree, he could soon be proved right.  

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