It's a day more than a quarter of a century in the making: On Saturday, European Commission chief Ursula von der Leyen is jetting off to Paraguay to sign the EU's biggest-ever trade deal with South America's Mercosur bloc . The EU is styling the megadeal as proof it can forge alliances and chart its own course in an age of disorder. But the pact remains unpopular with climate campaigners, farmers and EU heavyweight France — and could still be derailed when EU parliamentarians have their say in