The winner of this month’s Turkish presidential election will have to reckon with a dangerously lopsided economy that investors and economists say has veered close to the edge of financial stability.

Turkey will hold a runoff election on May 28 after neither President Recep Tayyip Erdogan nor opposition candidate Kemal Kilicdaroglu secured the 50% of the vote required to clench the presidency. Mr. Erdogan emerged with a convincing lead in the first round, a surprise after he trailed in polls in the days before Sunday’s vote.