Bush and the Republicans?

During the debates, why do Republicans never mention President Bush and continually avoid him even when he is brought up by the moderator? Instead, Republicans like to throw mud at Hillary, idolize Ronald Regan, (who served as President 22 years ago), and occasionally criticize President Clinton for decreasing the size of our military and for turning the Regan/Bush 10 trillion dollar deficit into a surplus after the Soviet Union had collapsed?