They used to giggle in Washington when somebody mentioned Scottish independence. Well, not anymore.

American foreign policy leaders are waking up to the prospect of the break-up of the UK, their oldest and, arguably, closest security partner. They are not happy; and they are starting to show it.

Some US newspaper editorials have thundered against Alex Salmond and his nationalist project. First the Christian Science Monitor warned the push for independence “sent a dangerous ‘go it alone’ message”.

Then the Washington Post said an “independent Scotland would significantly weaken the foremost military and diplomatic ally of the United States, while creating another European mini-state unable to contribute meaningfully to global security”.

Now Madeleine Albright, Bill Clinton's secretary of state, has  warned against what she called “fragmentation”. She told a Glasgow dinner: “In this day and age we have to all try to figure out how to work together, not so much separately.”

Scottish nationalists have been quick to play down US antagonism to their project. They - rightly - point out they have supporters as well as detractors across the Pond. But America’s foreign policy wonks are anxious.

So, they say, are the men and women they advise in the State Department and the Pentagon. Because suddenly – at least from a US perspective – the Scottish independence referendum casts doubts on old certainties, old alliances and old friendships.

Fiona Hill is director of the Centre on the United States and Europe at the Brookings Institute –one of America’s most prestigious think tanks. She has been flagging up the rise of the SNP for years.

“When I first raised Scottish independence in Washington DC, people just laughed,” she explains. “I think they were haunted by the spectre of William Wallace aka Mel Gibson going around in a kilt yelling ‘Freedom’. Whenever I raised the prospect of a referendum there would be an audible giggle.

“You could tell people were just not taking independence seriously and were looking at anybody who raised it as being, in their view, a member of the lunatic fringe. That has totally shifted.

“Now there is a sobering realisation that not just Alex Salmond means business but this whole discussion about the prospect of Scottish independence upends several decades of planning and US policy for a Europe that is free, whole and at peace. This is the crux of the problem; that the UK is no longer seen as a reliable security partner.”

Any rump post-independence UK, reckons Hill, could risk losing its permanent seat on the UN Security Council – starting a “food fight” over who replaces it.

Scottish independence, of course, throws up uncertainty over the future of the UK’s nuclear deterrent.

The SNP’s recent pained conversion to Nato membership post-independence hasn’t done much to assuage Washington policy-makers. They, unlike most of their citizens, are well aware of anti-American sentiment on the Scottish left, a left that may hold considerable sway in an independent Scotland.

The release of the only man ever convicted of the Lockerbie bombing didn’t help win the SNP or Scottish independence any American friends. The subtext is clear: a social democratic independent Scotland would weaken Anglo-Saxon conservatives in both in the EU in particular and the western alliance in general and strengthen the lefty, liberal Nordics.

That scenario, as this blog has reported before, can go down great in Copenhagen or Oslo.

But it is a harder sell in Washington.

Independence, insists Hill, is no longer a fringe issue in Washington. As Barack Obama begins his second term the future of the British union is beginning to force its way up his list of foreign policy priorities.

Hill explains: “Basically the State Department has realised Scottish independence is no longer in the purview of Mel Gibson. This could suddenly rise to the top of an agenda which is already overstrained as Americans worry about what this could mean for transatlantic alliance, for Nato, the European Union.”

Back in the 1990s Americans thought Europe was fixed. Communism had collapsed. New independent nations had emerged from the collapse of some of multi-national states of the east, such as the Soviet Union, Czechoslovakia and Yugoslavia.

Scroll forward a decade or two and – at least as seen from Washington – Alex Salmond’s SNP are threatening “stable borders” in the west of the continent. And not just in the UK. Why? Because the very fact a democratic independence referendum is to take place in Scotland – regardless of who wins it – can be seen as a licence for separatism across Europe.

Moreover, Salmond – with his civic, inclusive nationalism based on values rather than race – could be seen to be giving breakaway groups a new democratic legitimacy.The stories in the Washington Post and other serious US publications are not just about Scotland. They are about a “parade of separatism” from Barcelona to Brussels.

Hill continues: “What has got people’s attention here now is not just the push-up to the Scottish referendum but the broader implosion of the EU and the kind of shock that the UK and EU relationship is not what people thought.

“Salmond has cleverly shifted the discourse about independence away from nationalism, culture and language on to issues of political values, different fiscal aspirations and being more European than the rest of the UK.

“In doing that Salmond has upped the ante and in many respects provided a different pathway for other separatists in Europe. He has exacerbated a problem the US thought was at an end with the Balkan wars.Salmond has made separatism if not sexy then at least respectable again.”

So America isn’t just worried that Scottish independence will weaken its loyal British ally.

They are worried Scotland could begin a separatist process that would see the multi-national states of western Europe go the way of those in the east.

Remember most foreigners think of the UK, Britain, England as the same thing. What’s more, these islands are the home of “fair play”, democratic pedigree and political longevity.

That gives the Edinburgh Agreement and the prospect of a democratic divorce between Scotland and the rest of the UK an added oomph that no potential split in, say, Spain or Belgium would have. And the Americans know this only too well.

Hill also underlines worries in Washington that Scottish independence could unravel the Northern Ireland peace process.

Charles King of Washington’s Georgetown University has been at the forefront of explaining to America’s foreign policy community that Scottish nationalism is very different from, say, the issues in Northern Ireland.

In an article in this autumn’s Foreign Affairs magazine he underlined that Salmond’s vision of independence was far from the image of “blood and soil” separatism seen elsewhere.

But civic nationalism is hard to explain in America.

“The average American doesn’t think much of foreign policy at all,” concedes King. “But even among the foreign policy commentariat it comes as a surprise that Scotland has its own parliament and that there is a thing called the SNP pushing for independence. They can’t quite believe it because Britain seems like such a successful workable country, especially in comparison with other members of the EU.

“Britain’s standoffish stance to the Euro and sceptical look at Europe in general seems to many Americans to be the right attitude. To find a bit of the British electorate being more pro-European strikes many of us as strange. We are accustomed to thinking of independence movements as things that happen in places like South Sudan or Abkhazia or Kosovo. I have to explain that Scottish nationalism is of a very different stripe. But anybody is now in the position to use the Scottish vote in whatever way they want to support the politics of succession around the world.”

So how will America react to the independence referendum?

“With worry,” answers King. “The last thing Americans want is a Greece in northern Europe,” he says. “That is, a country that is less enthusiastic about the transatlantic alliance and that has a version of left politics that strikes many Americans as unworkable.”

The SNP, of course, would prefer to see Scotland as a rich and successive Norway or a Denmark than as a debt-ridden near-bankrupt Greece. The party, moreover, has committed itself to Nato – although this message has been slow to make it to America.

The Washington Post, for example, said Salmond’s “would-be country” (see, much as it pains Scots, some Americans don’t think we live in a “country”) would not be in the alliance. This in a leader written after the SNP’s conference in Perth had voted for Nato membership.

Would a Nordic pro-Nato stance for an independent Scotland go down better in DC?

“I think that is a reasonable pitch,” says King. “But the Nato decision looks like electoral opportunism rather than a considered approach to foreign policy.”

SNP leaders have persistently said that independence would mean America has two friends rather than one. But it’s a tough sell.

So what will the Americans do? Will old presidents be hauled out of retirement to make dire warnings? Would Obama intervene in the independence debate? Fiona Hill doesn’t think so. Neither does King. Nor anyone else I spoke to for this article.  America will - officially at least keep - its nose out of Scottish business.

“There will obviously be a lot of discouraging noises behind the scenes,” Hill says. “I think we will see more in the way of anxious questions being raised.”

Here’s the rub. Hill wonders if Americans have the “diplomatic wherewithal” to deal with Scottish independence. Do they know enough about this country to get to grips with the issue? For the SNP the same question – it seems to me - is even tougher.

I don’t know if American antipathy to independence will sway referendum votes. Some on the left will like the idea of winding up the Pentagon. Some floating voters may be scared off by US concerns about security. I don't know. 

Does the SNP or the Scottish Government – to use Hill’s expression - have the diplomatic wherewithal to assuage American concerns and silence those "discouraging noises"? Some nationalists routinely dismiss reports of international concerns about their independence project as unionist “scaremongering”.

My view: this will change. Because the SNP already has real enemies overseas – such as the arch-unionists of Madrid.  Of course, it also has potential allies too, not least in the capitals of northern Europe. Most Scottish nationalists, after all, sound more sympathetic to the EU project than their English counterparts.

But the time may have come for the Scottish government and wider national movement to relearn an art of diplomacy lost in 300 years of union.

Maybe Washington will see a tartan charm offensive?