Terrorism is beginning to disfigure the face of Europe. Besides the price of the carnage itself, terrorism is changing the character of Europe’s politics, threatening to make the arrangements of the EU look like utopianism, and leading to new restrictions and hassles for the lives of Europeans.

Tuesday’s terrorist attacks in Brussels, which ISIS claims as its own handiwork, killed dozens and injured hundreds. Officials there say they expected some kind of retaliation for the recent arrest of Salah Abdeslam, who was wanted in connection with last year’s attacks in Paris. Until more evidence surfaces, it is impossible to know if this attack was that retaliation or something planned further in advance. Police forces have also turned up evidence that Abdeslam was also planning an attack before his arrest, perhaps this one.

Belgium is a small country, and hundreds of its Muslim residents have traveled to fight in Syria for ISIS and then returned. The security and surveillance demands this threat imposes already overwhelm Belgium’s rather limited policing and intelligence resources. At a time when the problems posed by poorly integrated Muslim communities are leading to a renewal of Euroskepticism, the threats to Europe from within Belgium call for something like the opposite: more cooperation on security throughout the continent. How can Germany or France be doing their own job of protecting their citizens if, as last November proved, Belgium can be the source of serious terrorist threats?