Rattled by a newly aggressive Russia but still loath to confront the reality of violent conflict, Europe needs to draw clear lessons from the war in Ukraine in order to respond to a new and dangerous era, according to Donald Tusk, the former prime minister of Poland who took over recently as representative of the European Union ’s 28 leaders. Mr. Tusk, who will meet President Obama in Washington on Monday in his role as president of the European Council, said in an interview that Europe was not yet ready to further tighten sanctions against Russia despite continuing provocations by President Vladimir V. Putin. But he said he was eager for Europe to take a more robust stance alongside the United States in countering Russian efforts to redraw the borders of Ukraine, in dealing with chaos in countries like Libya, and in confronting the threat of jihadist […]