“THEY stayed a little back,” Donald Trump said about British and Nato troops in Afghanistan. “A little back”? Too many Brits never came back at all. Likewise Canadians. And Danes. And Australians. Too many Poles. Too many Estonians. In the dusty foreign fields of Helmand, Sangin, Lashkar Gah and Kandahar, they patrolled, cleared compounds, took…