European Union (EU) officials are worried U.S. President Donald J. Trump’s visit to Poland will bolster the populist, right wing government there, encouraging their defiance of the EU, and damage “European unity”. The president’s one-day stop-off – en route to the G20 summit in Hamburg – is for a gathering dubbed the Three Seas project, bringing together leaders from Central Europe, the Baltic States, and the Balkans. The event has been convened by Poland as it bids to garner influence outside the EU – which has clashed with its nationalist government over migrant policy and sovereignty. “One cannot but feel...