Complex sentence: His speech, aired live, implied that he would challenge the results in the Constitutional Court; the legality of such a challenge is questionable, as after withdrawing he is no longer considered a presidential candidate.
Split into simpler sentences: His speech, aired live, implied that he would challenge the results in the Constitutional Court. The legality of a Prabowo challenge is questionable, as--if he withdrew--he is no longer considered a presidential candidate.