A row over how to deal with child marriage among immigrants has inflamed political debate ahead of a general election in Sweden, where migration continues to divide public opinion and the far right is riding high in the polls. A tug-of-war between the ruling Social Democrat-Green Party coalition and the opposition over the government’s role in managing or eradicating the practice — which predominantly affects young girls, and in some cases boys, from immigrant backgrounds — is emblematic of a broader struggle to find a balance between efforts to integrate a large number of new immigrants and preserve a Swedish...