How has Danforth become a victim of his own logic?

Danforth has become a victim of his own logic, so to speak, when (in Act Four) it is now too late for him to do the right thing without losing his authority and calling into question the guilty verdicts of all those people who have already been hanged for witchcraft.  When he learns that two of the girls have stolen Parris's life savings and run away and that people in the town are close to rioting as a result of the more recent verdicts, he says to Hale that he cannot postpone because 

Postponement now speaks a floundering on my part; reprieve or pardon must cast doubt upon the guilt of them that died till now.  While I speak God's law, I will not crack its voice with whimpering.  If retaliation is your fear, know this -- I should hang ten thousand that dared to rise against the law, and an ocean of salt tears could not melt the resolution of the statutes.

He says that he cannot pardon or delay this day's hangings because it would not be just.  However, hanging any innocent person is not just!  But it is too late for him to even accept this as a possibility -- that they have condemned and executed innocents -- because there is nothing he can do about it now without undermining the court and himself.  He is trapped and can do nothing but move forward, even if that means he is hanging the innocent.