Since 2001, stem cell science in the United States has been explicitly constrained by federal prohibitions. Under an executive order announced by President George W. Bush on August 9 of that year, U.S. researchers can only receive federal funding for work done on the limited number of embryonic stem cell lines (an estimated sixty to sevent-eight) created prior to the executive order. Continued research on embryonic stem cells (ESCs) is not expressly prohibited. But, under the Bush administration's executive order, no federal funds can be used to develop new embryonic stem cells lines, or even to work on new lines developed after August 2001.
The problems with these restrictions, according to their critics, are threefold. First, they sharply limit the funds available to a high-cost, early-stage endeavor, limiting the pace of scientific discovery in the process. Second, they force stem cell researchers to maintain an administratively absurd line between research conducted in federally-funded laboratories (which include most university facilities) and that conducted in spaces free of federal funds.