It is not just Bosnia that is the problem, though with fighting still under way in the north-west of the country, continuing tension over eastern Slavonia and a renewed Muslim offensive on Mount Ozren, it is problem enough. Nato's top civilian official may be about to be charged with corruption, which will hardly help the cause when Bill Clinton goes to Congress to seek approval for deployment of 25,000 US troops. And the mission that Nato has been handed is riddled with paradox and contradiction.
Making peace stick in Bosnia is the biggest challenge that Nato has ever tackled, and there is little time to get its act together. "If the peace talks proceed quickly and get a peace agreement in, say, early November, Nato would have to be prepared to make a very rapid deployment of its forces," said William Perry, US Defense Secretary, this week.
"We are in a race against time," said French Defence Minister Charles Millon. This will be far more complex than the air strikes carried out against Bosnian Serb targets, and it must be sustained for a year.
It was desperately ironic that just as it undertook this operation, Nato's Belgian Problem should raise its head once more. The Belgian Problem is called Willy Claes, and he happens to be the secretary-general of Nato. On Friday, radio reports said that Belgium's top court had recommended that Mr Claes should be charged with corruption in connection with his time as Belgian economics minister.
This will not help Bill Clinton. It was never going to be easy to persuade Congress of the neccessity for ground forces in Bosnia, something the US has steadfastly resisted up until now. "We've got a good deal of consulting, a good deal of explaining to do on Capitol Hill, and acquainting the American people with the basis for such a decision," said Warren Christopher, US Secretary of State. this week. He added that a refusal to participate "would be the end of Nato".
"I have pledged to consult with Congress before authorising our participation into such an action," said Mr Clinton in a major foreign policy speech. Thus far, almost alone of the international organisations of which the US is a member, Nato has remained above partisan politics and above the kind of nationalist criticism which the UN has attracted.
Mr Claes - never as popular with Congress as his German predecessor, Manfred Worner, may now have become such a liability that he has to go before Congressmen start asking some difficult questions about Belgian politics.
But the difficulties go beyond one man and his past. A Congressman with a good research staff and a questioning mind might also raise some other concerns about the apparent contradictions in the way Nato's mission is framed.
The rhetoric is of "overwhelming force", for instance, with military sources talking of thousands of troops pouring over the borders into Bosnia within hours through five routes. The aim, said Mr Perry, is to have "the biggest and meanest and toughest force in the area".
But diplomats also say that this force cannot exist without some form of "strategic consent" from the warring parties, implying that there are clear limits on how this overwhelming force can be used.
The mission in Bosnia is, in theory, a strictly neutral task to enforce a peace agreement. But the US is also talking about bolstering the abilities of the Bosnian Muslims and Croats to defend themselves, through a general "build-down" of weapons if possible, through training and assistance if not, something that worries the European members of the alliance. Throughout the Bosnian war, there has been unhappiness in Paris and London about US motives and - despite the need for public unity now - that has not gone away.
There is also the nagging question of the Russians. It is vital to both the alliance and Moscow that the new force integrates in some shape or form a Russian element. But Russia has no desire to serve under Nato; and Nato is pledged to maintain sole control of the military aspects of Bosnia, an apparently unsquareable circle. Today, Mr Perry will try to keep the Russian relationship on track at a meeting in Geneva with Pavel Grachev, Russian Defence Minister. Russia is threatening to boycott joint exercises later this month in the US, and continues to make its unhappiness known over Nato plans to expand its membership. Keeping Moscow onside over Bosnia is vital for the longer-term aim of rebuilding European security with Nato at its heart.
So Bosnia presents the alliance with the biggest political challenges it has ever faced. Yet the events of the last few weeks - massive air strikes, a renewed US diplomatic commitment to Bosnia and preparations for the new force - have come about partly because America was so concerned that if Nato did not act then the risks were greater. Nato had to show itself to be vital, or at least relevant, or risk fading away.
Nato has always been part of a triangular relationship, with the Europeans, Americans and Russians at each apex. Keeping that triangle stable is getting harder and harder. Six years after the reunification of Germany, five years after Iraq invaded Kuwait, four years after the end of the Soviet Union, three years after the beginning of the Balkan conflict, two years after Nato decided to enlarge and one year after its aircraft began strikes in Bosnia, the alliance is still peering into the darkness to see where it is going. The plunge that it is now making is a leap of faith.