Hillary Clinton's popularity continues to slide as she takes on a more political posture and Republicans raise questions about the deadly 2012 attack on a U.S. diplomatic post in Libya on her watch.

Fifty-two percent of Americans view the former secretary of state favorably, down from 56 percent in March and 70 percent in December 2012, according to the Bloomberg National Poll.

The decline means Clinton wouldn't enter a possible 2016 race as a prohibitive favorite over key Republican rivals. While she still bests them in head-to-head matchups, she doesn't have majority support against any of them.