Late in the day, an increasing number of American politicians and academics are wondering if it is a good idea to expand a NATO alliance which was set up to contain a hostile Soviet Union that no longer exists.
The 16 NATO governments have already agreed to open the alliance doors to Poland, Hungary and the Czech Republic in a first-stage expansion which could yet embrace the rest of Europe, but the US Senate could kill this move by refusing to ratify the enlargement treaty this week.
This is unlikely to happen, as the Clinton administration is confident it will get the necessary two-thirds Senate support for enlargement, but alarm is now being expressed that the serious issues at stake have not been properly debated.
Critics argue that the decision to expand the original Cold War alliance will increase instability inside Russia as NATO creeps closer to its borders. The architect of the old "containment" policy, the former diplomat Mr George Kennan, has condemned expansion as a historic blunder.
The senators themselves are asking questions about the wildly varying estimates of the costs of expansion, ranging between the latest, at $1.5 billion over 10 years, to $125 billion over 15 years. They are also facing criticism from their constituents about allowing the US to get drawn into central European quarrels like those in the Balkans and being reminded what this could cost in US lives.
Senator Pat Moynihan, a leading Democratic Party intellectual, made a speech last week entitled "Could NATO expansion lead to nuclear war?"
The New York Times has long been unhappy with the prospect of enlargement, warning that it has not been properly debated and "may damage the country's paramount security interests for decades to come". The newspaper says that President Clinton and his aides "mistake Mr Yeltsin's acquiescence for permanent Russian acceptance".
The prospect of NATO forces moving closer to Russia's border is making it place "greater reliance on its nuclear weapons as a first line of defence" while in the Russian parliament it has stalled a treaty to reduce stocks of nuclear weapons, the Times argues.
The Clinton administration waves aside such criticism, which is coming from both liberals and conservatives. The present US ambassador to NATO, Mr Alexander Vershbow, rejects claims that there has been inadequate debate. More than 1,000 articles have been published in the past 18 months on all aspects of NATO's evolving role; 300 conferences on enlargement have been held in Europe and North America; and there have been 12 hearings before Congress in the past six months, the ambassador says.
He rejects the argument that enlargement will "poison relations with Russia". This might be true if NATO were seeking to isolate Russia, "but the opposite is the case".
"Through the Partnership for Peace and the newly established NATO-Russian Permanent Joint Council, NATO has created a network of security co-operation that has engaged all the states of Europe, even former neutrals," he argues. In fact Ireland is one of the very few countries which has not engaged in this network.
While the Senate will probably ratify the treaty with up to 70 votes (67 will be required), according to its Republican leader, Senator Trent Lott, there could still be several amendments forced on the Clinton administration.
Senator John Warner, who supports enlargement, wants any further expansion frozen for three years. Other central European countries and the three Baltic states are also candidates.
Other proposed amendments would delay NATO membership for Poland, Hungary and the Czech Republic until they join the EU, put limits on the US financial contribution to enlargement and bar expansion of NATO's mission beyond the collective defence of its members.