According to Zakaria, the way Saddam's trial was mishandled has its roots in the ill-advised decisions of the White House:
... the Bush administration dismissed the idea of trying Saddam under international law, or in a court with any broader legitimacy. This is the administration, after all, that could see little advantage to a United Nations mandate for its own invasion and occupation.
It put Saddam's fate in the hands of the new Iraqi government, dominated by Shiite and Kurdish politicians who had been victims of his reign. As a result, Saddam's trial, which should have been the judgment of civilized society against a tyrant, is now seen by Iraq's Sunnis and much of the Arab world as a farce, reflecting only the victors' vengeance.
This was not inevitable. Most Iraqis were happy to see Saddam out of power. .... This was so even among Iraq's Sunni Arabs.
... But during those crucial first months, Washington disbanded the Iraqi Army, fired 50,000 bureaucrats and shut down the government-owned enterprises that employed most Iraqis.
In effect, the United States dismantled the Iraqi state, leaving a deep security vacuum, administrative chaos and soaring unemployment. That state was dominated by Iraq's Sunni elites, who read this not as just a regime change but a revolution in which they had become the new underclass.