FOR a Dutchman driving his caravan to the Costa del Sol, the only thing to remind him that he had crossed borders used to be the successive text messages welcoming him to Belgium, France and Spain. That was before this summer’s migrant crisis—and last weekend’s terrorist attacks in Paris. Now the liberty to roam the 26 countries in the border-free Schengen zone, which Jean-Claude Juncker, the president of the European Commission, calls a “unique symbol of European integration”, is under greater threat than at any point since its inception.

Calls to curb borderless travel were already growing louder in August after Ayoub El Khazzani, a Moroccan national, carried an assault rifle across two borders on a Thalys train before attacking fellow passengers. In September Angela Merkel, Germany’s chancellor, warned that without agreement on how to handle refugees they would grow louder still. The overwhelming scale of migrant arrivals led several countries, including Hungary, Slovenia, and ultimately Germany and Austria, temporarily to reintroduce border controls. Sweden, then getting 10,000 new arrivals each week, joined them on November 12th. The Netherlands has doubled its spot checks in the border area since September. And Denmark’s announcement that it will introduce electronic number-plate scanners at border crossings strains the limits of the Schengen framework.

The attacks in Paris have changed the debate. Ever since it became clear that the terrorists had strong links to Belgium, Peugeots coming over the border from Brussels have seemed just as great a threat to France as planes flying in from Damascus. As investigators retrace the movements of the terrorists and their weapons, more intra-European links will surely be uncovered, and more of Schengen’s weaknesses.

After last week’s attacks, France swiftly reinstated border checks at major crossings. The Schengen framework allows such temporary measures for national security; the French had been planning the move anyway for a UN climate conference in Paris later this month. Now they are pushing for more. At a meeting of justice and home-affairs ministers in Brussels on November 20th, France will ask that Europe start to collect passenger name records from those travelling within the region—which it has pressed for since the Charlie Hebdo attacks—and for further exchange of data through the Schengen Information System, a security database. France will also demand a true Europe-wide agency to police Schengen’s external borders. François Hollande, its president, said he wanted a Europe of open borders, not a continent of “walls and barbed wire”.

But others disagree, especially in the east. Hungary has already built a 100-mile fence along its Serbian border. Austria is planning one on its border with Slovenia. Slovakia’s prime minister, Robert Fico, says he too is ready to build fences (the security of Slovak citizens “is a higher priority than the rights of migrants”). After the Paris attacks Poland’s minister of European affairs declared that the EU’s deal to redistribute asylum-seekers was off. Slovakia’s election campaign has become an anti-migrant shouting match. Hungary’s prime minister, Viktor Orban, blamed migration for the killings in Paris. (He also said it increased rape and threatened Europe’s culture.)

In western Europe, right-wing populists are playing on the public’s fears. Nothing helped their cause more than the (unconfirmed) report that one of the Paris gunmen entered Europe through Greece, posing as a Syrian refugee. Marine Le Pen, who has warned for months that jihadists are posing as refugees, claimed vindication. Matteo Salvini of Italy’s right-wing Northern League repeated his call for the suspension of Schengen. In polls taken since the bombings, 70% of Dutch people say the borders should close.

Fear and loathing are not the sole response. On November 15th Germany’s interior minister, Thomas de Maizière, urged the press and society not to link the attacks to the refugee debate. The dominant line in talk shows in Germany and much of western Europe is that the refugees are victims of Islamic State’s terror, not perpetrators. Recep Tayyip Erdogan, Turkey’s president, an unlikely but necessary ally of Mrs Merkel’s, said at last week’s G20 summit that treating refugees as terrorists would be “evading humanitarian responsibility”. One important meeting was Mr Erdogan’s with Alexis Tsipras, Greece’s prime minister, on November 18th; their shared border is among the most porous on Schengen’s periphery. Until the zone’s external borders are secured, freedom of movement inside it will be in danger.