"Assault Weapon" is an arbitrarily defined term meant to engender fear in the uninformed. It is used to define many firearms which are functionally the same as any number of semi-automatic sporting rifles.
Furthermore, weapons which were defined as "assault weapons" by the last AWB accounted for less than 5% of firearms related homicides. The president already acknowledged that AR-15 and AK-pattern rifles were not involved in most violent crime in this country during the presidential debates.
The proposed Assault Weapons Ban takes the focus of the real issues in the wake of national tragedy. There are a host of other issues relating to violence in this country that are more timely and worthy than pushing for another AWB, which will do little else than disarm law-abiding citizens.