A Brexit warning from one prime minister to another
Forget about the tangle over the Irish border for a moment.
The prime minister could hardly have been clearer that she will reject the EU's position today. The lines are drawn for a fight over the draft treaty that will run for many weeks.
But there are broader concerns that it's not just that issue that's extremely hard to solve, but suggestions today that the government's whole approach might in fact be an impossible compromise.
The former Prime Minister, Sir John Major, is often mocked by some of his former colleagues. A veteran of course of his own battles with Eurosceptics, among Brexiteers his views are derided.
His speech today may even be seen in some quarters as part of a Remain plot - Brussels, the Labour Party and political bigwigs somehow working together to thwart Theresa May.
But his strongly-worded plea for Parliament to be given more power over Brexit, and his criticisms of the government's approach, may crystallise the concerns that many Tories have, and likely, some members of the public too.
- Give MPs free vote on Brexit deal - Major
- May: UK cannot agree to EU Brexit draft
- Why English courts are opening in the EU
- Brexit: All you need to know
His essential case? That the prime minister this time round relies so much on the support of "ultra Brexiteers" as he calls them, that she is heading for a deal that could harm the country, with no consideration for reasonable compromise or pragmatism.
In that case, he is urging her to give MPs a vote on the final deal, with the power to reject it, and even potentially give the country a say too on the final deal in a second referendum.
It won't take long to cue calls of voter fatigue, interference from the establishment, or a refusal from Remainers to accept that they lost the argument in 2016.
But today's call from Sir John will give succour to those Conservatives who have been pushing for Parliament to be more vigorous in making its views heard, and urging Number 10 to take more account of those trying to find a middle ground.
And just at the moment when Theresa May is trying to inch her party forward, a warning, from prime minister to prime minister, not just that her approach is wrongheaded, but that her ultimate goal may be impossible to achieve.