Open this photo in gallery: Karol Nawrocki and his wife Marta Nawrocka in Warsaw Sunday.Aleksandra Szmigiel/Reuters Conservative historian and staunch nationalist Karol Nawrocki has scored an upset victory in Poland’s presidential election and dealt a blow to the centrist government of Prime Minister Donald Tusk. Mr. Nawrocki won 50.89 per cent of the vote in Sunday’s election while Warsaw mayor Rafal Trzaskowski took 49.11 per cent, according to Poland’s National Electoral Commission. The result marks a stunning turnaround for Mr. Nawrocki, a political novice who is backed by the populist Law and Justice party, or PiS. He trailed Mr. Trzaskowski...