MAGDEBURG, Germany—Chancellor Angela Merkel’s conservatives looked set for a resounding victory in a state election in eastern Germany on Sunday, in a boost to Armin Laschet, who hopes to succeed her in September’s national election. An exit poll for public broadcaster MDR had the Christian Democrats (CDU) on 36 percent, up more than six points on five years ago, and far ahead of the far-right Alternative for Germany (AfD), who were on 22.5 percent, slightly down on the previous election. Laschet, long-serving premier of the western state of North Rhine-Westphalia, was seen as having made an uncertain start to his election campaign and had been facing calls to chart a more right-wing course to win back voters disenchanted by Merkel’s 16 years of centrism. Casting his vote, state premier Reiner Haseloff had presented himself as the candidate of the center around whom those opposed to extremism could rally. “This will …