Spanish Prime Minister Pedro Sánchez called China's trade imbalance with the European Union "unsustainable" on Monday, as he began a three-day visit to Beijing where he hopes to strengthen economic ties. Sánchez's visit is his fourth to China in four years as he seeks to position Spain as a bridge between Beijing and the 27-member European Union, whose relations with the United States show signs of strain. US President Donald Trump's tariffs and unpredictable foreign policy have caused concern among Western leaders, many of whom — including from Britain, Canada and Germany — have flocked to Beijing, in recent months…