BUDAPEST, Hungary — Few leaders have done more than Hungary’s Viktor Orbán to shape the global right-wing populism that informed President Donald Trump’s MAGA project. On Sunday, Orbán faces the biggest challenge of his 16-year authoritarian rule as Hungary goes to the polls for a parliamentary election. It has been a febrile campaign, with allegations of “false flag” operations, wiretapping and even an alleged sex tape plot. Usually, an election would pose little risk for Orbán. The leader goes into Sunday’s vote as the great survivor on Europe’s political stage, holding power since 2010 thanks to four back-to-back victories, each...