Beyond the Supreme Court ruling and the savage polarisation of the British body politic, there are two key questions for Ireland and the EU.
Is Boris Johnson serious about reaching an agreement with the EU by the October European Council?
If so, what will that deal look like?
Let's take the second question first.
Under Boris Johnson, the UK has abandoned some of the core objectives of the backstop: protecting the all-island economy, north-south cooperation, the integrity of the single market and avoiding a hard border and related checks and controls.
"The objective for the UK now," says an EU official closely involved in the negotiations, "is to have as invisible a border as possible and reduce friction where you can. But there would still be, to all intents and purposes, a regulatory and customs border on the island of Ireland."
The UK has put forward four technical "non-papers" in recent weeks, essentially testing ideas with the EU without committing to them.
The main idea is an all-Ireland agri-food and animal health zone, aligned north and south under EU rules.
This formed part of the original backstop.
However, whereas the original envisaged broad alignment on other single market and customs union regulations, Johnson now wants alignment to be restricted to agri-food, and what are called sanitary and phytosanitary (SPS) checks and controls.
That would still leave industrial goods, customs, state aid and VAT rules. If those rules were different north and south there would be a regulatory and customs border.
Under current UK proposals that problem would be addressed by technology, trusted trader schemes, exemptions from EU law and other facilitations, all worked out during a transition period after the Withdrawal Agreement was ratified.
However, EU officials say these are simply "concepts" and the UK does not regard them as needing to be legally operable until later.
The reason agri-food plays such a crucial part in the negotiations is because of its role in cross-border economic activity.
Some 30% of milk produced in Northern Ireland is processed in the south, converted into milk powder, infant formula or other dairy products such as butter and cheese, and either sold into the EU, transported to the UK, sent back up to Northern Ireland, or exported to the rest of the world under EU trade agreements.
One third of the pigs produced in the south are slaughtered in Northern Ireland, and up to 400,000 sheep from the north are slaughtered and processed in the south, and sold on to the French market.
These are just two examples. Keeping the whole island within the realm of EU agri-food (SPS) rules makes sense according to the logic of the backstop, since all of that trade would be produced under the same rules thereby avoiding the need for food safety and veterinary checks at the land border.
There would, however, need to be controls on such consignments coming in from Great Britain to Northern Ireland, since Great Britain would be outside the single market.
The latest UK non-paper on how addressing that issue has raised alarm in Brussels.
Officials from 27 member states briefed on the the fourth technical paper were told that not only had London de-coupled SPS from all other economic activity, but British negotiators also wanted a selective approach to SPS rules.
The six-page paper set out three categories of SPS rules: those checks and controls which the UK accept would need to be applied on goods coming from Great Britain into Northern Ireland ports; those checks which do need to apply, but which could be applied "away from" the land border; and those checks which the UK believe do not need to apply at all, such as the requirements for food products to comply with EU labelling rules.
The EU has immediately dismissed this as cherry-picking.
"Cherry-picking is intrinsically problematic," says one official briefed on the UK paper. "There's a reason why all these things are interrelated. They are there for a purpose.
"If you start cherry-picking SPS rules, why are you doing it? What is the purpose, from an Irish point of view? What does it mean for divergence [from EU rules] and what impact is it going to have on the all-island economy?"
But what caused more irritation was the fact that the UK appeared to be lecturing the EU on what food safety rules they felt should or shouldn’t apply, or which were genuinely needed in the Irish context.
"The fact is that the UK - another country - is nitpicking on SPS rules, effectively second-guessing the EU’s approach. It’s something we’d reject on principle. It’s not for the UK to start defining what our approach is and whether it makes sense or not. The bottom line is: if Northern Ireland is within our SPS zone, the whole of the SPS rules should apply."
Furthermore, said the source, the UK’s approach raised questions about how it would behave in negotiations on a future free trade agreement. Essentially it set a precedent of the UK judging whether EU rules were valid or not.
The other problem, and one which will loom large, is the link between the EU’s SPS regime and customs.
According to officials, there is an important intertwining of the EU’s customs rule-book (the Union Customs Code), and SPS rules.
Strictly speaking, both things are separate.
Ensuring that food coming into the EU is safe for consumers is the responsibility of officials from departments of agriculture across (currently) 28 member states, who follow a voluminous EU rulebook.
Only when agriculture officials or veterinary inspectors are satisfied that importers are complying with the rules will customs permit the consignments to enter.
"EU law says SPS products cannot be allowed into the EU by customs until they’ve been cleared by the SPS authorities," says an Irish Revenue source. "That’s what the law says."
However, on the ground there is an operational link between customs and SPS controls, which the European Commission is intent on preserving.
"Customs and SPS work very closely," says a senior EU official. "They’re at ports, major rail crossings, airports. They very often share IT systems. The pre-notification of live animals, animal products, often initially would go to both customs and SPS services.
"In addition you very often rely on customs for on-the-ground intelligence and checks, because not all trade happens as it should. Customs might open up a container and find food products in it. In those circumstances they’ll turn to their veterinary colleagues and say, we need you here."
A diplomat from one member state says: "The customs authorities get all the information on incoming goods. It’s completely integrated with regulatory controls and market surveillance. It’s the key channel for all information for incoming goods."
That is why there is a juxtaposition of customs and SPS infrastructure, personnel and IT systems on all EU-third country frontiers.
If the EU agreed to the British request of partial alignment by Northern Ireland to EU agri-food regulations, but not to customs, it would mean stand-alone SPS controls at Northern Irish ports and airports, but with no accompanying customs presence, since Boris Johnson is insisting that Northern Ireland remain part of the UK’s customs sphere.
That means there would be no bank of intelligence or data, such as normally provided by customs, monitoring what was coming in.
Not only that, the UK papers, according to sources, do not spell out how those SPS controls would operate.
In principle, the controls should be manned by EU-mandated officials, as they would be applying controls under the EU rulebook.
"From the [non]-paper it’s not clear how information would be channeled, how checks would happen, how enforcement would happen. It’s just not providing the confidence required," says one EU source briefed on the latest UK paper.
The belief in Brussels, therefore, is that customs will be the battleground over the UK’s attempt to replace the backstop.
"The key issue will be customs. Where will the money be collected? How is it going to be collected?" says one senior EU official.
Customs is more intimately linked with sovereignty. Theresa May’s negotiators objected to Northern Ireland on its own being part of the EU’s customs territory under the original backstop proposal, so they pushed for a UK-wide customs union, uniting the EU’s customs territory and the UK’s customs territory for a temporary period.
This, of course, fell foul of Brexiteers who argued it would prevent the UK from having its own independent trade policy.
Having rejected the temporary customs arrangement, it seems unlikely that Boris Johnson would go for anything that ties the UK to an EU customs sphere.
All this, of course, depends on whether or not Boris Johnson wants a deal, which brings us back to the first question, and whether or not realistically there is enough time to reach that agreement.
Brussels and Dublin have been willing to give the prime minister the benefit of the doubt. However, member states are hardening their position.
The proposals so far fall well short of the backstop’s objectives, and London’s insistence that the non-papers be kept from officials from member states has soured the mood.
"The parties are still far apart from each other," says one member state official.
"The timeline is tight, to put it mildly. When you work on the basis of non-papers which the UK shares with the commission but are not sent to member states, it means we can’t check the detail or ask questions. It’s not helpful."
Several officials believe the technical talks in Brussels are essentially a holding pattern ahead of the Conservative Party conference next week.
"I think after the conference things will move," says a senior EU source. "They don’t want the conference to be taken up with all sorts of conversations about papers being tabled."
However, after the scenes in the House of Commons on Wednesday night, in which Johnson goaded the opposition and appeared to take a cavalier approach to the murder of Jo Cox MP, pessimism has increased.
To get a last-minute deal through the House of Commons Boris Johnson will need the support of his own backbenchers and a clutch of Labour MPs from Leave-voting constituencies.
"The performance of Boris Johnson was not lost on us," says one EU official.
"What this means is there is no chance in hell that he’s got a majority [to pass the deal] at the end of October. You don’t get to antagonise the opposition benches, but also your backbenchers in that way. He’s not trying to demonstrate to us that he is serious about getting a deal. You don’t burn bridges like that. You can see the flames from afar."
Until Wednesday, some officials believed that Johnson could pirouette back to the Northern Ireland-only backstop once the Tory Party conference was out of the way, with some assurances for unionists on oversight and involvement by the Northern Ireland Assembly.
But that too now seems a forlorn hope. The appetite for the EU to be flexible on the backstop has been intimately linked with Johnson’s ability to get the agreement through parliament. If there’s no prospect of that, there’s no reason to be flexible.
Boris Johnson is therefore unlikely to take any risks with his party and the core target of Leave voters by tilting at a deal at the European Council.
Under the Benn Act, Johnson will then be obliged to seek an extension.
Given the severity of the UK Supreme Court judgement it seems inconceivable that he would flout the law.
He could face not only criminal charges, but also civil personal liability, given the exposure of UK firms to the collateral damage of a No Deal exit.
The options therefore narrow further.
Johnson could either reluctantly seek an extension, blaming parliament and the EU for the state of affairs, or he could get another minister to send the written extension request, or he could step down as prime minister and pass the chalice over to a divided opposition.
Either way, an election would be inevitable. However, Number 10 knows Johnson’s prospects are far from certain given the threat posed by Nigel Farage’s Brexit Party.
"The Boris bounce hasn’t been big enough," says Paul McGrade, of Lexington Communications, a former Foreign Office official currently advising clients on Brexit.
"Most of the polling would suggest the Brexit Party are still in double figures, and it seems as there’s still a reasonable chunk of Brexit Party supporters who don’t yet trust him or the Tories to deliver the kind of Brexit they want."
As such, Johnson’s doubling down on the aggressive rhetoric is designed to peel Leave voters back to the Tories through the "people versus parliament" narrative.
He is also appealing to the considerable number of British voters who are jaded and alienated by the antics in Westminster with the mantra that people just want to "get Brexit done".
But as Theresa May discovered in 2017, an election strategy can badly backfire.
Assuming the EU grants an extension at the end of October, a Johnson majority would in theory permit him to get a post-election deal through the House of Commons without depending on the DUP.
That might give him more flexibility in the negotiations, but if the EU insists on a fully fledged backstop, albeit with some oversight concessions for the Northern Ireland Assembly, Johnson would still end up with a deal not entirely unlike what Theresa May negotiated.
That might fall foul of the hardline ERG within his party and other unionist-minded Tories.
If Johnson fails to get a majority the outcomes would be a Labour government, which most observers believe is highly unlikely, or a hung parliament. Out of some permutation a second referendum cannot be excluded, but that would take six months to organise, well beyond what the EU might be prepared to offer by way of an extension.
So the EU’s nightmare scenario is further gridlock and instability with the grace period provided by an extension period rapidly running out. Even if it is determined to avoid taking the blame for a no-deal exit, the EU would eventually have to draw the line and refuse to grant any further extensions to Article 50.
In the current agonies of UK politics the only certainty is that the country is ossifying into furious and irreconcilable blocs of Leavers and Remainers, with very few voters amenable to having their minds changed by reasoned debate.