ISTANBUL — President Recep Tayyip Erdogan has long made clear that he considered no part of Turkish life beyond his reach, not least the economy.

Even before he was re-elected in June with sultanlike powers, he had built his popularity on sustained economic growth fueled by signature megaprojects — the latest being plans for a canal bisecting the country. But critics have long charged that much of that expansion was built on budgetary sleight of hand, cronyism and corruption.

Now Turkey’s worst economic crisis since 2001 — the currency hit another new low on Monday — has confronted Mr. Erdogan with the limits of his authoritarian approach and could end his long run of success.

It is also fanning fears of a global contagion, as Turkey’s troubles undermine investor confidence in other emerging market economies and raise concerns about the exposure of banks even in developed regions, like the European Union.