Rabbi Akiva (in Talmud Sanhedrin 90a) contends that when the Torah speaks of this prophet performing miracles, the prophet was then a true one. Only later did he deflect to the wrong path. Once becoming a false prophet he is no longer able to perform miracles. As Rabbi Avi Weiss extracts, this answer underscores a critical concept in Judaism, especially as the month of Elul, the thirty days of introspection before the High Holidays begin: notwithstanding one's achievement or spiritual level there is always the possibility of failing (i.e. false prophet), and an equal possibility of improvement (i.e. Teshuva (repentance) before Rosh Hashana)! While the Parsha depicts a prophet that has fallen from grace, rising to grace is just as viable. Just like the prophet, we are judged based on where we are now, and how much we've improved, not on where we once were.