Krauthammer sums it up pretty nicely:

In fact, Bush's case was simply a more elaborate and formal restatement of Bill Clinton's argument in 1998 that, left unmolested, Hussein would "go right on and do more to rebuild an arsenal of devastating destruction. And some day, some way, I guarantee you, he'll use the arsenal."

That was true when Clinton said it. It was true when Bush said it. The difference is that Bush did something about it