Organizers of a potential science debate between leading US presidential candidates have not given up on hopes for it to take place in Philadelphia on 18 April — even though Barack Obama and Hillary Clinton (pictured) have agreed to participate in another, non-science debate in the city two days earlier.

With the Democratic primary race so tight, the stakes are high for the 22 April Pennsylvania primary. Obama has also agreed to a debate in North Carolina on 19 April, before the 6 May primary there.

Organizer Shawn Otto says that supporters still hope to hold a science debate to raise the profile of science and technology issues in the campaign. They hope to hold the debate in Philadelphia's Franklin Institute.