Mr Obama faces a tricky task in nominating a candidate who will not prove too liberal on abortion to gain Republican support and so avoid a filibuster.

Obama could define the debate further - and demonstrate his professed support for the bureau - by going on the offensive and nominating Ms. Warren as its official director.

Mr Reed then had the idea of changing the primaries so that they ceased being a "nominating process" and became instead a simple mechanism to find the top two vote-getters.