Good move! He just raised the stakes for a debate with Mrs. Bill Clinton. He’ll shame her into a debate, with no way out. The pressure is on her to perform, and we all know how that will work out...cough cough.
He doesn’t have to shame her into a debate. Presidential candidates are expected to debate each other at least once or twice
He shouldn’t have said he would debate Sanders in the first place, but backing out makes him look cowardly. A successful capitalist with reasonable speaking skills should be able to out-debate a failed socialist easily.