Despite victory in the gulf war George Bush's approval ratings decreased this was because

inability to contain a worsening recession.

Explanation:

Despite having the highest approval ratings of 80 percent in Gallup polls history at the time, which was mainly influenced by the United States victory in the Persian Gulf War, in 1990. George H. W. Bush, approval ratings decreased at alarming rate as a result of worsening economic situation of the United States, particularly on increase in the rate of unemployment, which eventually led to his defeat during his second term bid.

Hence, despite victory in the gulf war, George Bush's approval ratings decreased this was because " his inability to contain a worsening recession."