I like this part of Boris’s letter to Donald Tusk:
This government will not put in place infrastructure, checks or controls at the border between Northern Ireland and Ireland. We would be happy to accept a legally binding commitment to this effect and hope that the EU would do likewise.
The jurisdiction with fewer regulations has nothing to lose from such an arrangement, of course. The EU bureaucrats, however, want to be in control, and a source of cheap goods from a free-er jurisdiction must make them uncomfortable (as well as being highly profitable for Northern Ireland). Leaving the EU to build their own border infrastructure is the default position for the UK anyway: the UK cannot lose. This is a test of the EU’s commitment to free trade, as opposed to “free trade” as controlled by them.
The letter is only about the backstop. Theresa May’s agreement minus the backstop still has many problems. It remains to be seen whether Boris and Parliament will settle for it.