tough enough?

From a New York Times article about Barack Obama’s riding high in the race for the Democratic nomination:

He lists the arrows that critics sling his way. He’s too hopeful, too inexperienced, not tough enough. At mention of the last, he bobs his head, steps toward the crowd, leans in and says: “Listen, I’m a black guy named Barack Obama running for president. You want to tell me that I’m not tough enough?”

He smirks. “Shoot.”