How many Europeans now favour Schengen? How many now favour greater state powers to intercept our e-mails and mobile phone calls? How many suddenly have qualms about letting large numbers of migrants from the Middle East into their countries?
And what does this all mean for the future of Europe, Britain's place in the EU, and Poland's new government? Five events stand out as significant.
1) The Kalashnikovs used in Friday's murders are said to have come from the Balkans. Criminal gangs there are making money selling automatic rifles and rocket grenades to Islamist murderers. Once inside the Schengen area, the weapons passed freely all the way to Paris via Brussels. Schengen's border with the Balkans runs through Slovenia and Hungary. Now, both countries have put up anti-migrant fences along their southern borders to cries of outrage from the well-meaning European left. But how many of them now feel a bit more secure now that a well-worn gun-smuggling route has been cut? The happy notion of open borders between Schengen members is beginning to look like becoming an anachronism.
2) One of the murderers, it is suggested, had entered the EU as a refugee from Syria, passing through Greece in September. How many more 'sleeper' ISIS terrorists have slipped into the EU posing as migrants? Alright, the vast majority of those refugees are fleeing the same murderous thuggery as Paris experienced last week. But if even 1% of those hundreds of thousands seeking asylum in the EU are ISIS sleepers, or simply have the potential to be radicalised, then yes - many more people today are thinking it's better to be safe than sorry than thought this last week.
3) Solidarity with the people of France - Wembley Stadium - scores of thousands of Englishmen singing the Marseillaise and shouting 'Vive la France!' is moving. How many of them were hitherto Little Englanders with a less-than-secret liking for Nigel Farage? The evacuation of central Hanover this evening shows that the threat hangs over the whole of Europe. So - shared insecurity and feelings of solidarity are bringing Europe closer together emotionally, while at the same time the same fears are closing European countries off from one another physically.
4) Russia draws world attention away from its crimes in Eastern Ukraine, as Putin talks about cooperating with France to punish the perpetrators of last month's terrorist bombing of a Russian passenger jet killing 221 civilians over Sinai. Russia's early intervention in Syria was mainly directed at anti-Assad rebels rather than ISIS. The attack on Metrojet Flight 9268 is another factor changing things. Putin changing his spots? Don't be taken in, West. Today, Ukraine reported 25 ceasefire violations in the Donbass.
Foggy days and Warsaw's airports
This time five years ago:
Local elections - the lure of ultra-localism