Could the migration crisis finish the EU?
Hardened Eurosceptics might love to think the EU's in trouble, but as leaders gather in Brussels for their summer summit on Thursday, dedicated Europhiles are also sounding the alarm.
"The fragility of the EU is increasing," warns EU Commission chief Jean-Claude Juncker. "The cracks are growing in size."
In the meantime, there is no whiff of EU agreement over what to do with migrants who do reach Europe.
Which brings us back to the threat to Schengen.
Gloomy German government sources told me they gave the project a three out of 10 chance of survival thanks to the increasingly nationalistic nature of many European governments.
"And if Schengen does fail," they predict, "that would be the beginning of the end of the European Union."