Sentence:  "The 2½ years since have been about hammering home these points in any European capital that would listen. And in spite of capacity-sapping talks on the first point – Brexit, border and <WSD>backstop</WSD> – the Department of Foreign Affairs and other government departments have been working quietly to make good on the second. 
Meaning of the word marked with <WSD> tags:  A default arrangement that holds if all else fails.