In 2001 George Bush signed an executive order banning federal funding for embryonic stem cell research, except for those lines that were already established. As a result such research ground to a halt in the US.
While the order was presented as a compromise, the effect was chilling in its application. No researcher receiving federal dollars (even for a separate project) could do embryonic stem cell research, except on the approved lines. Institutions could not risk losing federal grants and so had to purge themselves of any banned research. The approved lines did not turn out to be as useful as was originally claims, and they became progressively obsolete as new techniques were being developed through state and private funding.
It is impossible to measure the effect that Bush’s ban had on ultimate scientific progress in this area. It is not just that we lost eight years – expertise in a cutting-edge scientific area can be a tenuous cultural and institutional thread, once broken it is difficult to recreate.
We will hopefully have a chance to find out. It was expected that one of the first measures of the Obama administration would be to lift the federal ban. In fact, I am a bit surprised it has not happened already. But it seems it soon will – insiders are saying that Obama plans to lift the ban soon.