The last time a bill supporting human embryonic stem-cell research was introduced to the US House of Representatives, it was co-authored by a seasoned Republican congressman from Delaware. Announcing the bill in March, Mike Castle hailed President Barack Obama's executive order that lifted restrictions on federal funding for the controversial research, and declared that "Congress must act to ensure that an over-arching ethical framework is signed into law."

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Castle, who gave up his House seat to run for the Senate, lost his party's nomination to Tea Party-backed opponent Christine O'Donnell. O'Donnell is against stem-cell science, which some equate to abortion — a deeply divisive issue in US politics. This is reflected by a state ballot that would grant human rights to embryos from the moment of their creation (see 'State watch: Colorado').

Even more worrying for researchers is a lawsuit that seeks to suspend federal funding for the research. The case could overturn guidelines implementing Obama's order as early as next month. That possibility has advocates calling for Congress to pass the Castle bill, co-sponsored by Diana DeGette (Democrat, Colorado), during its post-election session, before the new congress is seated.

"Should there be an adverse ruling blocking stem-cell research, certainly there would be much more pressure on Congress to act," says Tony Mazzaschi, the senior director of scientific affairs at the Association of American Medical Colleges (AAMC) in Washington DC. Earlier this month, the AAMC asked its members to contact their representatives, urging them to use the session to enact the bill.

But with a long list of priorities demanding time during the dying days of the current Congress, lawmakers may not manage to deal with the stem-cell bill. And should the House or Senate swing to the right in the election, stem-cell legislation may falter in the next Congress — despite having passed twice in the past, only to be vetoed by then-president George W. Bush.

Castle's is not the only departure that will be keenly felt by the National Institutes of Health (NIH), by far the largest funder of US biomedical research. David Obey (Democrat, Wisconsin), chairman of the powerful House Committee on Appropriations that allots money for the NIH, is retiring. In the Senate, Arlen Specter (Democrat, Pennsylvania), who last year won an additional $10.4-billion allocation for the NIH in return for supporting Obama's stimulus bill and later switched parties to join the Democrats, lost his new party's nomination.

Even with Specter and Obey still in place, the current Democrat-controlled Congress is struggling to deliver the 3.2% boost to the agency in 2011 that Obama requested last winter. A Senate committee passed the $1-billion increase in July, but the bill has not come to a vote in either the House or the full Senate. When lawmakers reconvene after the elections, NIH advocates may not be able to withstand relentless pressure to curb non-mandatory spending. "We are going to have to work hard to make the case that NIH deserves an increase while other things are being cut," says Jennifer Zeitzer, a lobbyist for the Federation of American Societies for Experimental Biology in Bethesda, Maryland.