Its more than that. The backstop has become a handy shorthand and lightning rod for a 700 page agreement they haven't understood and probably haven't even read. While lots of different Brexiteers have lots of different problems with different parts of the agreement, they have decided to coalesce around this one issue. This has the benefit of making a deal easier to come by IF the timing is right (last minute) and Brexiteers don't have time to then move on to other gripes as it reduces all opposition to one core fault.

So if, for example, Johnson decides to ditch the DUP and make the backstop Northern Ireland only, everyone bar the DUP and a v. few hard core British unionists are happy - and the deal is even better from an Irish/EU perspective as they were never happy to guarantee the UK cost free access to the Single Market and Customs Union in the first place.

If the DUP do decide to press the nuclear button (at the risk of putting Corbyn in power) Johnson can campaign on the basis of a new improved deal which no longer keeps GB tied to the EU indefinitely.  Everybody suddenly thinks the other 699 pages of the agreement are great, breaths a sigh of relief that no deal has been averted, and gives Johnson an electoral endorsement if the Telegraph's opinion poll is to be believed.

Obviously the Brexit party will campaign on the basis that the other 699 pages aren't great either and so it will become a no deal versus Johnson's deal debate with Labour and Remainers sidelined. Johnson will seek to capture the "reasonable" centre ground and campaign on the basis that his deal will allow the UK negotiate its own trade deals and control immigration.

Corbyn will find it hard to differentiate himself from that position because in practice Labour differences with that are small and relate to the yet to be negotiated future relationship part of the deal. Johnson can fob off those concerns by promising to negotiate a pony for everyone in the next phase. And many will believe him...

Index of Frank's Diaries