Why was Labour punished in local elections?
At the end of today, the Tory party will have had a terrible night - perhaps losing as many as 1,000 councillors in England, compared with a worst-case projection (by Tory peer Rob Hayward) of 800 defeats.
But that may not end up being the big news: it is not exactly a revelation that vast numbers of Tory supporters are incandescent that the prime minister has failed to deliver Brexit yet.
A majority of Tory MPs wanted Theresa May to resign before yesterday's elections; they still want her out. Nothing has changed, as she would say.
Much more significant is that Labour too is losing seats. And even though the attrition is much less than for the Conservatives, Labour should not be losing any councillors against a floundering government mid-way through a parliamentary term and given that the comparator is a 2015 poll when (under Ed Miliband) it performed poorly.
What is not yet crystal clear is precisely why Labour is doing so badly. Labour's shadow chancellor John McDonnell concedes the cause is the Brexit uncertainty, but that is to obscure as much as to reveal.
Or to put it another way, is Labour being punished for being too Brexity, too Remainy or simply too ambivalent on the biggest issue facing the UK?
It is not even clear what is going on in one of the great Brexit heartlands, Sunderland, where Labour lost 10 seats. The leader of the council Graeme Miller blames the perception in the north east that his party does not really want the UK to quit the EU.
But while there may be many Wearsiders who mistrust Labour's Brexit credentials, and while it is true that a depleted UKIP did make three gains in Sunderland, the cheerleaders for a Brexit referendum, the LibDems and the Greens, also picked up five seats between them.
Sunderland seems to be as divided and confused as the rest of the country.
It also matter that nationally, the Lib Dems and Greens have performed strongly. But the definitive verdict on what has really gone wrong for Labour will have to await a detailed and forensic analysis of whether the damage to the party has been done more by desertions of supporters to pro-referendum parties or by the disillusionment of working class and left-of-centre Brexiters.
Only then will it be clear whether Labour MPs like Jess Phillips have a point when they call for Labour's "triangulation" of Brexit, its attempt to please both Brexiters and Remainers, to be dumped in favour of what they see as a more principled position of backing a confirmatory Brexit referendum.
That verdict will have consequences for Theresa May too - because it will determine whether Jeremy Corbyn will be more or less enthusiastic about agreeing a Brexit compromise with her in coming days.
As of first thing this morning, Labour leadership was agonising about whether signing off a Brexit pact with the government that contains a Customs-Union element would permanently alienate millions of pro-referendum internationalist supporters and would be seen as propping up an ailing Tory government, or whether it would end all the noise that makes it impossible for the country to hear the party's message for social and economic change.
So these local elections will reverberate even to those parts of the UK, like Scotland, Wales and London, where they didn't take place.