Why are Britain and the EU still fighting over Brexit?

“Get Brexit done” was British Prime Minister Boris Johnson’s slogan when he ran for election two years ago.Since then, Britain has pulled out of the European Union after more than four decades of membership and several years of wrangling over divorce terms.And yet the quarrels go on. The UK and the EU of now 27 nations are once again trading accusations and insults as they try to resolve rough spots in their relationship.What’s the problem?The current conflict centres on Northern Ireland, the…