Top economist Mohamed El-ErianPhoto by Rob Kim/Getty Images The Federal Reserve is once again having to resolve a complex set of problems, according to Mohamed El-Erian. 'It's a trilemma — inflation, growth and financial stability," the top economist told CNBC. But there's no "first best policy response" the Fed can take amid the banking turmoil, he said. The Federal Reserve is once again juggling a complicated "trilemma" of problems — but this time, there's no good policy move it can make in the fallout from banking turmoil, Mohamed El-Erian has warned.