By  Simon Nixon

The heart of the Brexit debate was over how Britain could best maintain its status as a core rather than peripheral country in Europe. Brexiters claimed the U.K. could never be central to the European Union while remaining outside both the eurozone and the border-free Schengen travel zone. Remainers argued the U.K. played an outsize role in shaping the EU—not least in creating the single market, supporting the EU’s eastward expansion and helping shape its trade policies—and that it was quitting the EU that risked turning Britain into a peripheral country.

This debate has acquired a new relevance following Emmanuel Macron’s victory in the French presidential election on Sunday, but not for the short-term reasons one might think.

Much time has been devoted in recent days to examining the entrails of Mr. Macron’s campaign pronouncements to divine what his election augurs for the prospects of a Brexit deal. But this is the wrong question. Sure, the election of his rival, Marine Le Pen, would have been a disaster for the U.K., plunging the continent into chaos, sapping the EU’s political capacity, and increasing the risk of a disorderly Brexit.
But the handover from President François Hollande to Mr. Macron should have little bearing on the negotiations. France’s interest will remain the same: preserving the integrity of the European legal order. The outcome of Brexit talks won’t hinge on some political deal between Prime Minister Theresa May and Mr. Macron, but on how much of that European legal order Mrs. May is willing to retain in return for special partnership that allows Britain privileged access to European markets and security arrangements—even if it means the U.K. would no longer have a say on formulating those rules.

The real significance of Mr. Macron’s election for the U.K. lies not in his influence over Brexit but over the future of the EU itself. One of the most powerful arguments put forward by Brexiters in last year’s referendum was that there was no risk to quitting the EU because it was about to fall apart anyway: The real risk, they said, was to stay on board the sinking ship.

Following Mr. Macron’s election, this argument looks far harder to sustain. The EU now looks unlikely to collapse, at least in this electoral cycle. Instead, Mr. Macron wants to reform France and the eurozone in ways he believes will make the EU stronger. Of course, that won’t be easy. Powerful French unions are already signaling their readiness to resist his planned overhauls of the labor system and public sector. And his proposals for a eurozone budget and treasury will run into opposition from Germany, which at the very least will insist on further pooling of sovereignty as the price of any deeper fiscal integration. Even so, one shouldn’t underestimate the degree of consensus across the eurozone that further measures are needed to strengthen the single currency. And the success of Ms. Le Pen and other populist parties in Europe has provided a sharp reminder of the price of failure.

What should most concern the U.K. is Mr. Macron’s influence on the EU’s future commercial policy. Mr. Macron is a liberal and a globalist, as he memorably demonstrated during the campaign when engaging with workers from a factory facing layoffs. But he is a French liberal, who as economy minister increased the French state’s stake in car maker Renault, giving it the power to block a merger with Nissan . And while he strongly opposed Ms. Le Pen’s calls for greater protectionism at a national level, he favors greater protection at a European level. His manifesto included a “Buy European Act” designed to level the playing field with the U.S. and China in public procurement markets. He also favors greater controls on foreign investments in strategic sectors, demands that EU free- trade deals include binding social, environmental and fiscal commitments, and proposes creating a European commercial prosecutor to ensure these commitments are met.

Perhaps these proposals will come to nothing. A Buy European Act has been on the table in Brussels since 2012, with the latest version stalled in the European Council, in part due to British opposition. But Mr. Macron’s manifesto is a reminder that protectionism can take many forms. It should surprise no one that European politicians, like their American counterparts, are engaged in a debate about free versus fair trade and talk of the need to ensure greater reciprocity in trade deals to maintain public confidence in globalization. Even the U.K. government, which claims to be a global leader in free trade, dropped its opposition to stiffer anti-dumping measures against subsidized Chinese steel following the threatened closure to the Port Talbot steel works.

The risk for the U.K. is that it won’t be at the table when these policies are debated, making it more likely they will be adopted in ways that harm British interests. Of course, this was precisely what led successive U.K. governments to spend a decade trying to join the European project in the first place. Now, far from escaping a burning building with Ms. Le Pen supplying the fuel, the U.K. faces a future on the periphery of a potentially stronger and more cohesive EU that may use its commercial policy more assertively. That may not be a comfortable place to be.