After the Democrats turned Vietnam into a quagmire Nixon showed the North Vietnamese he could be more brutal than they were. Nixon ended the draft and actually turned 90 percent of the war over to South Vietnam. When the South Vietnamese fought back a major NVA offensive the Democrats couldn't stand it. With Nixon gone they cut off all military aid and naval and air support to the South. The next Soviet-backed NVA invasion succeeded and Nixon's legacy was further tarnished.
Obama has approached Iraq in the same way. If Iraq succeeds as a democracy Bush will get credit. So Obama is determined, in his passive/agressive approach, to undermine Iraq.