When will gene therapy be common in the us, and why was bush so opposed to it?

Gradually. Bush, who had no personal stake in this being devoted as he was only to money, was advised to stop stem cell research and gene research by his advisors to appease the ignorant feelings of the right wing religious fanatics in his party. Note that while they controlled all govt. Branches, they did not introduce bills on the subject. They want them around to collect votes and money.
Hard to say when. Gene therapy is a huge ethical dilemma in this country tied to the idea of when life begins. If you believe that life begins when a sperm fertilizes an egg, then you would agree with bush that stem cells from embryos constitute murder of an unborn child. However there are safe alternatives from stem cells harvested from bone marrow. Until an agreement can be made on which to use, we'll be in limbo.
He wasn't. Gene therapy itself is not to be confused with embryonic stem cell therapy. Gene therapy is curing important diseases such as hemophilia b without anyone presenting a religious objection. Now that the safety and likely effectiveness of embryonic stem cells for am important form of blindness seems to be near-future, rhetoric from religionists may be up for reconsideration.