The olive branch Jeremy Corbyn has extended to Theresa May could save or destroy her.
Just to be clear, his offer is what some in her cabinet, and many on her benches, in Whitehall, in Brussels and in EU capitals have been mooting as a Brexit compromise that would solve both the Northern Ireland backstop and the future relationship.
It would see the EU concede a circumscribed common rulebook for goods while she sacrificed the right to do third-party trade deals.
Many of her Remainy MPs would buy that. And with Labour’s support that deal would obtain parliamentary approval.
But perhaps 100 of her Brexiter MPs would never vote for it. They might even quit the Tory Party rather than be associated with it.
So Corbyn has set May up to choose between a negotiated Brexit and splitting her party.
Which sets up next week’s Tory conference as perhaps the most important of the modern era.
Because it may determine both what kind of Brexit she can negotiate and whether the Tory party can survive any kind of negotiated Brexit.