The rift between the Americans and the French and British over Bosnia has become perhaps the most serious row ever in the alliance. The Americans are on their own, with no friendly words from London. The special relationship is not only not special, but in the last week has not been much of a relationship at all.
The UN and Nato have been here before, as is painfully evident. In April the eastern Bosnian enclave of Gorazde collapsed after Nato and the UN proved unable to agree on the terms to protect it. That lesson was supposedly learnt, and a flurry of activity resulted. This weekend, again, Nato aircraft buzzed Bosnian Serb forces but failed to attack because there were no targets designated for them by the UN.
Nato has spent its existence preparing for a very different task: the military defence of Western Europe. It has had enormous problems getting used to the circumstances of Bosnia, and in particular working with the UN. But the real problem is not the military. ''There are two Natos,'' says an alliance source - the integrated military command and the political alliance. It is the latter that has failed. There has been and is no consensus on what kind of war is raging and what kind of response it requires.
During 31 months of fighting in Bosnia, the alliance has zig-zagged its way through a political minefield, marching to the sound of the guns and then marching back again. Last Thursday, it came unstuck in a fairly spectacular fashion when a US plan to save Bihac was kicked around an airless conference room in Brussels for nine hours and then left to die.
The American plan was to turn Bihac into an exclusion zone, allowing the Bosnian troops in it to leave with their weapons, and to enforce it with air strikes in and outside the zone. With close-quarter battle going on around Bihac, air strikes there would risk hitting the wrong targets and the US suggested applying pressure by hitting other, ancillary targets elsewhere. The allies rejected it because they were unhappy with the idea of an exclusion zone, and disturbed by the wide-ranging plans for the use of air power. But the real sticking point was the lack of troops to enforce the exclusion zone.
The US has refused, since the beginning of the conflict, to put ground forces into Bosnia. That is still the case. But Pentagon sources indicate that the Marines in the Adriatic will be available to rescue UN or Nato personnel in the region. Administration officials are refusing to clarify, however, whether they would be allowed to go ashore to carry out any rescue missions, for example. Washington is stressing, meanwhile, that the decision is not a sign of deepening US involvement in the conflict.
It fears that large-scale deaths - or even relatively modest losses, such as those suffered in Somalia - could result in a political backlash.
As the security situation deteriorates, calls for disengagement will be heard in countries with commitments to Unprofor. It is a grim and darkening situation. Just over the horizon is the threat of America lifting the arms embargo. The spectre of a complete breakdown, with government and Bosnian Serb troops turning on the men in blue helmets, is getting closer.
Therein lies the real reason why the US Marines may be needed. In the event of an evacuation under fire - Nato is committed to help. It has drawn up scenarios under which 20,000 or more troops could be called on to help get UN peacekeepers out, and that would be a Nato operation, under Nato command. US troops would be involved. But that would be for the salvation of 12,000 British, French and other peace-keeping forces, not for the people of Bosnia.
Such a withdrawal risks being triggered by the US, if it carries out its threat unilaterally to violate the international arms embargo against the Bosnian Muslims. Much may depend on the attitude of the soon-to-be leader of the Senate, Bob Dole. Mr Dole is expected to hold critical meetings in the next few days with Nato officials in Brussels and John Major in London.
President Clinton is anxious to forestall Republican-led pressure from Capitol Hill to supply arms to the Muslims, putting him at odds with many in Congress. The keenness of some lawmakers to supply arms to the Muslims may have been cooled in recent days after warnings from Pentagon officials that it may cost millions of dollars and inevitably involve US troops in the region.