UK negotiators take the position that an EU-UK free trade deal to be agreed in 2021 will take care of the Ireland-NI border issue.

But (not unreasonably) the Irish government wants the Brexit treaty to provide an independent guarantee of an open border should the post-Brexit-transition free-trade deal not work out.

Because the continued existence of PM Theresa May's UK government depends on support of the pro-British NI DUP, Ms. May has had to reject an earlier EU proposal that NI remain under EU trade rules post-Brexit.

A hard Ireland-NI border would do serious damage to tourism in both countries, and in the worst case could result in renewed sectarian violence in the Island of Ireland.