From terror squads who slip past border controls to the valiant but all-too-improvised emergency response, the backstory of last week's attacks in Brussels is eerily similar to what happened in the United States in the leadup to September 11, 2001.
Virtually every mistake made then by the US national security machine found its analogue in Belgium on March 22. Now Europe's leaders need to work out their own answers to those challenges while overcoming particularly European obstacles. Until they do, their citizens will remain exposed to the next atrocity.
While much has been made of Belgium's failings - the split between Dutch- and French-speaking subcultures, interlocking layers of government that obscure accountability, the neglect of aggrieved Muslim communities - they are a microcosm of what Europe has to contend with. National security in the EU is just that: a national prerogative.
It comes down to "typical gumshoe detective-type work", said Colin Clarke, a terrorism researcher at Rand Corp in Pittsburgh.
"European intel services definitively have more suspects that they need to track, monitor and surveil.
The sharing within Europe sometimes seems to stop at the border, while terrorists don't."
The EU appointed its first anti-terrorism co-ordinator in 2007, in a bid to step up intelligence efforts in response to the bombings in Madrid in 2004 and London in 2005. Yet European agencies are still engaged in the turf battles that absorbed CIA and FBI attention in the runup to 9/11.
To take one data point: an estimated 5000 European citizens went on jihadist junkets to join extremist groups like Isis (Islamic State) in Syria and Iraq, but there are only 2786 in one database, 1473 in another, and 90 per cent of the names added recently came from only five EU governments.
"Some continental intelligence agencies jealously guard their secrets," said Sajjan Gohel, international security director for the Asia-Pacific Foundation in London.
"Often they have a piece of the puzzle that if they put it together, they form a wider picture of what the network actually looks like."
The potpourri of European watchlists includes Focal Point Travellers and the European Information System, both managed by Europol, the EU's police-co-ordinating agency; the Schengen Information System and Visa Information System, used by national police and border patrols; Eurodac, a roster of applicants for political asylum; ECRIS, a repository of criminal records; and a nascent database of air passenger profiles, modelled on the US tracking system.
The air-traveller monitoring system proposal has also been around since 2007, blocked by the European Parliament on personal-privacy grounds until the Paris killing spree in November forced it back onto the agenda.
Even now, some EU MPs are stalling the measure until more data-protection safeguards can be introduced, in another example of the peacetime priorities prevailing over security concerns.