How to judge Sunak's Northern Ireland Brexit deal

Rishi Sunak today embarks on an adventure in political and economic jeopardy, the magnitude of which he has never encountered before.

At the very least, his amendments to the Northern Ireland section of Brexit - the notorious Protocol - will define the first period of his time as PM, and perhaps his entire premiership.

He'll be judged on three questions.

First, and for Northern Ireland's Democratic Unionist Party (DUP) and the Tory Party's Brexiter European Research Group (ERG), it's all about whether Northern Ireland will move decisively out of the constitutional and legal ambit of Brussels.

Sunak will make that claim.

He will point to:

• Practical changes which eliminate most physical checks on goods and foods, flowing from Great Britain to Northern Ireland for so-called trusted traders;

• Sovereignty changes which will mean if VAT or duties are cut or subsidies increased in a Westminster budget they will apply in Northern Ireland;

• A consultative mechanism which will shrink the so-called democratic deficit in Northern Ireland - that's been created by the province remaining in the EU's single market for goods - by giving members of the Northern Ireland Assembly a voice - though not a veto - on new Brussels laws, which relate to the manufacture of goods in the province;

• Judicial changes which reduce the likely frequency of the European Court of Justice being brought in to determine whether single market rules are being properly applied in Northern Ireland.

So, how will the DUP and the ERG - and the rest of us - assess Sunak's claim that he is yanking Northern Ireland back into the UK fold?

It's all about the legal standing of the texts which are published today, whether they represent formal, unambiguous, permanent definitive change to the Brexit treaty. Or whether they are clarificatory and amplificatory side texts that remain vulnerable to legal interpretation.

For what it's worth, DUP sources tell me they will take days to determine whether Sunak's deal does what he'll insist is written on the tin. So it will be some time before we know whether the DUP is prepared to end its block on the devolved government in Northern Ireland - though my hunch is the DUP will ultimately be disappointed and the Assembly and Executive in the province will NOT belatedly be reconstituted.

Judgement number two on all this will be around whether it opens an important and friendlier chapter in the UK's post-Brexit relations with the EU, which will lead to more constructive co-operation on immigration questions, notably the small-boats crisis in the Channel, defence co-operation and trade.

Finally, there's the narrower judgement - though the one that's arguably more important for Sunak - which is whether what's agreed today reinforces or heals the ideological and tribal splits in the Conservative Party.

That boils down to the verdicts of two former prime ministers: Liz Truss and Boris Johnson.

If they say that everything announced today by Sunak was available to them, but was rejected by them as inadequate, then the factionalism in the governing party will worsen.

So, somehow Sunak will have to prove, beyond reasonable doubt, that his Protocol deal is not only a decent enough deal, but one that was uniquely available to him. That's not easy in a party where the language of political and personal betrayal infects everything and everyone.

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