And is impossible. We're not just talking about trucks of washing machines travelling 3,000 miles, we're talking about cash-and-carries feeding stores half a mile away, about cattle crossing the "border" for slaughter, about milk moving from the udder to the tanker to the dairy, about all the trade movements that go on at a town level but with an arbitrary border through the middle. No credible system has been proposed that can electronically or remotely perform veterinary checks on moving animals or people's carrier bags.
It's not "impossible" - just fraught with difficulty... but it needn't even be the case.
The EU could have committed to agreeing to maintain the status quo under Article 24 of the WTO rules, which allows an interim trade pact to persist for up to 10 years while a permanent agreement is made. The EU and the UK could then commit to a formal trade deal to guarantee tariff-free trade between the EU and the UK, thus rendering most of the problems with the Irish border moot. But the EU are loathed to do that because they consider that too much like the UK having access to the Single Market without being a member.
The fundamental problem is the fact that Ireland and the UK already have an unbreakable bilateral agreement that scuppers the EU's requirement for a hard border in Ireland. But the authors of the Good Friday Agreement did not take into account the possibility (and indeed the right) of either Ireland or the UK to exit the EU - as a result, it is now a problem for all sides to figure out how to keep the border open when the UK and Ireland's status as EU members is no longer the same.
By far the most sensible solution all along has been for the EU and the UK to strike a new trade deal that eliminates tariffs and keeps as close alignment on standards as possible - not that hard given that the UK is currently an EU member and has all EU standards already incorporated into UK law. Of course, over time there will inevitably be some divergence, but surely it is not beyond the wit of man to figure out a solution that doesn't mean installing a hard border in Ireland. Indeed, it is not a question of 'maybe' - there must be a solution found sooner or later.
It must be remembered that the UK always had and always will have a sovereign right to leave the EU. The EU's own acquis enshrines that very right. Ireland is a special case (though arguably similar problems would arise upon another member's exit) and thus requires special consideration. Frankly, however, the EU's proposed solutions are nothing short of disgraceful and it is no surprise that they've been roundly rejected by the UK Parliament.
And that's what the war was about. And that's where we're returning to. It doesn't take a big leap of the imagination to think that Crown customs offices are going to be a target. Then the targets have to be protected, and then the British Army are performing "peace patrols", and then the walls come back up (some never came down on certain streets, of course), then we're back to the troubles of the twentieth century.
If parties in the EU want to try to avoid that on behalf of the GFA and honour the spirit of it (no hard border is a clear interpretation of that spirit, imo) then they can only entertain solutions that keep NI in a borderless trading solution. It's not their fault that Brexit was a **** idea based on an ongoing three-year series of inflammatory untruths.
Well, exactly.
But a huge part of the problem is the EU's dismissal of the most obvious possible solution and their sequencing of events. As it stands, the EU requires that an exiting member state agree to a permanent default solution (the backstop) before even allowing trade negotiations to begin! Frankly, that's inane - and it is little wonder that the process has been a total failure given that the backstop effectively breaks up the exiting member state.
Worse still, the EU have been pretty clear that they have no intention of offering the UK a free trade deal that keeps trade across the Irish border tariff-free. And even worse still, they have also stated that a No Deal exit means negotiations are over and that any future trade deal requires the UK to accept the unacceptable Withdrawal Agreement first. That is ridiculous, and it is also totally counterproductive to their (supposed) aim of "doing all" to keep the Irish border open.
If the EU were sincere and serious about 'doing all' to keep the Irish border open after Brexit, they should, at the very least, be considering a free trade deal with the UK to be put in place as quickly as is legally possible.