IT'S BUSH'S FAULT.
Bush was a nice guy, but he was out of his league. He got his dad's looks, but his mother's (lack of) brains. Reagan came into office along with 192 Republican congressmen and when he left, there were 175, a drop of 17 seats. In 1978, before Reagan was elected, there were 158 GOP congressmen in office, so you could say that Reagan's coattails amounted to 34 seats.
Bush came into office along with 221 GOP congressmen and when he left, there were 178, a drop of 43 seats. In 1998, before Bush was elected, there were 223 GOP congressmen in office, so Bush actually had coattails amounting to -2 seats. Bottom line is that Bush did nothing for the GOP in coming to office and trashed it on the way out.
Bush was an irresponsible moron who raised welfare state spending via Medicare Part D, No Child Left Behind and the stupid homeownership program that resulted in the mortgage crisis of 2008. And the funny thing is that liberals hate this guy every bit as much as they hated Nixon, another big-spending Republican. And the sad thing is, the alternative to him in the GOP was McCain. Running for office is such a difficult, specialized and thankless endeavor that no competent businessman wants to try and the one who did was a dilettante prone to saying politically-disastrous things for no good reason. Romney said very little, but the few things that he said sank his candidacy. Brilliant guy, but a tone-deaf political moron.