The key concern, the Israelis said, is where the jihadis go after Assad falls. Do they stay on in Syria to fight any Alawite militias that may appear? Do they go west to Lebanon, to fight the Shiite group Hezbollah? South to try to cross into the Golan, and fight the Israeli army? Or east into Iraq, to fight as Sunnis against the Shiite-led government of Prime Minister Maliki — which the Israelis saw as perhaps the most likely outcome?

But there is another possible outcome: that the jihadis go to Europe to commit acts of violence and terror there. Why would hundreds of them possibly go to Europe? Because they came from Europe.

The facts are pretty clear: There are hundreds and hundreds of European Muslims now fighting in Syria. When I met recently in Washington with the top civil servant in one of Europe’s foreign ministries, this was his greatest fear: What will they do when they come “home,” their fighting skills now honed through months of combat alongside other jihadis from Libya, Pakistan, Afghanistan, Iraq, and many other countries?