Governments and scientists worldwide will welcome indications that the United States is once again considering participation in ITER, the international project to build an experimental magnetic-confinement fusion reactor (see page 247).

If the United States does rejoin the project, it will send important political signals to the nation's allies, who are concerned about the unilateralist leanings of George W. Bush's administration. ITER is also the largest example of a research project pursued as a genuine collaboration between the world's major scientific powers. In most 'big science' initiatives, such as the US-led International Space Station, other partners have assumed a secondary role. But future projects in disciplines such as high-energy physics will require cooperation on equal terms, and ITER provides the only extant model.

ITER is also important because any real exploration of long-term, sustainable energy must include a thorough technical evaluation of nuclear fusion. Despite theoretical doubts about the ability of a doughnut-shaped magnetic chamber, or tokamak, to contain plasma, such a device remains the best prospect for tapping fusion power.

Before hopping back into bed together, however, the United States and its former partners need to take a careful look at what led to their 1999 estrangement.

Encouraged by the doubters in the US fusion-research community, Congress had lost patience with ITER. The project's management must share the blame, having failed to adapt its design proposal to fiscal realities — not just those in the United States, but those in Europe, Japan and Russia, too — until forced to do so. ITER also failed to sell itself to the public, as any big-ticket project must do in a democratic society.

Bush would do well to buy back into ITER, and to help to rebuild it as a model of scientific collaboration. The mercurial power of Congress to abruptly end funding will remain a threat — reforming the US budget process to provide some security of funding for the nation's international commitments may be just as challenging as containing plasma at a temperature of one million kelvin. In the meantime, ITER's management must do a better public-relations job, and ensure that it does not become distanced from its political paymasters.