Brussels attack raises the chances of Brexit

To stem the flow of migrants–and that criticism–Merkel has cut a deal with Turkey. She has offered, among other things, visa-free travel within the Schengen area for 77 million Turkish citizens. This deal will likely unravel as it fails to slow the arrival of migrants, and mistrust between Europe and Turkey’s government will grow. Now there’s a new set of terrorist attacks to add to Britain’s worries.

A vote for Brexit is a leap into the unknown. It would force the British government to renegotiate trade and investment relationships with other E.U. governments, which will make the bargaining as arduous as possible to discourage other members from leaving. That process will generate enough uncertainty to create serious problems for Britain’s growth. It would prove much more difficult for Britain to win access to European services markets, and E.U. leaders likely won’t allow London to remain the region’s financial center. Brexit also might give Scottish nationalists the argument they need to hold another vote on independence–and this time to win it.

Polls are close but swinging toward exit. The danger is that with the public divided, the passion of the anti-Europe side will carry the day. The cold economic logic favoring remaining in the union won’t do much to excite voters who are seeing constant headlines about how Europe is falling apart. Prime Minister David Cameron has acknowledged as much, saying this month that his biggest concern was low voter turnout for the “in” campaign.