President Bush’s approval rating fell at the end of his presidency in part because

Bush’s approval rating declined after he broke his 1988 campaign promise, “Read my lips: no new taxes,” and agreed to a tax increase in 1990. The economy also entered a recession, adding to public dissatisfaction. The other choices do not fit: the United States won the Persian Gulf War, and the Panama invasion and Oklahoma City bombing were not the main causes of his declining approval.

AI-written and checked against the verified answer.