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On Thursday, the United States celebrated its independence from the United Kingdom.

On Monday, it will try to codify its interdependence with the European Union by negotiating a transatlantic trade pact.

That chat might be a bit awkward. A recent report published in the German newsmagazine Der Spiegel alleges that the United States spied on its E.U. allies in diplomatic posts in New York, Washington and Brussels. The allegations are just the latest diplomatic damage done by Edward Snowden, the former U.S. intelligence contractor gone rogue.

In private, European politicians are probably not surprised. But in statements, they've reflected public anger.

"If the allegations prove to be true, it would be an extremely serious matter which will have a severe impact on E.U.-U.S. relations," said Martin Schulz, president of the European Union.

"Partners do not spy on each other," said Viviane Reding, the European Union's commissioner for justice.

But apparently they do, and have been for a long time: The practice predates President Obama. "It's unpleasant to learn that your friends are listening to you. But I doubt any of them are shocked," said Frances G. Burwell, director of the program on transatlantic relations at the Washington-based Atlantic Council.

In fact, added Burwell, Europeans may be more surprised by the scope of the NSA's metadata mining methods, which Snowden revealed via London's Guardian newspaper.

So far the focus has been on the NSA, but after the Parisian paper Le Monde reported on Thursday that France intercepts Internet and phone data, the focus may shift inward, too.

Burwell said that the strong reaction has historical roots. "Europe has relatively strict privacy controls over the collection of data. And this is particularly sensitive because of the misuse of that type of data by both Nazis and communist regimes."

The first rough draft of history — journalism — has reflected, and to some degree led, European outrage, too.

"For the media, it was a great kind of moment," said Jan Techau, director of the European Center for the Carnegie Endowment for International Peace. Based in Brussels, Techau said that Europeans went through a "first wave of rage." But now coverage is "moving from breaking news more toward essayistic 'what does it mean?' 'Is this Orwellian?' 'Is the open, liberal society in danger?' 'Is America really standing for the values it claims to stand for?' "

This last question should be the first thing U.S. leaders ask themselves, because in a post-9/11 world of asymmetrical threats and international institutions like the United Nations paralyzed by Chinese and Russian recalcitrance, the United States needs NATO partners more than ever. Especially if it adopts a "lead-from-behind" leadership style like it did in the intervention in Libya. Squandering the "special relationship" with the United Kingdom and solid relationships with other European Union nations by bugging buildings in Brussels is letting tactics trump strategy.

"NATO is an alliance, and an alliance has to be built on trust as much as anything else. And when you strain the trust among nations that are part of an alliance, you strain the alliance, too," said J. Brian Atwood, former dean, and now professor, at the Humphrey School of Public Affairs.

This strain comes amid "an interesting phase in transatlantic relations," said Techau, who like Burwell cited NSA surveillance, drone policy and the Guantanamo Bay detention center as reasons Europeans have cooled on President Obama.

"Those that are politically interested and had such high hopes for Obama to be a different kind of politician are now really disappointed that he is a just another president," said Techau, who said it could translate into an "America skeptical" (not anti-American) sentiment. "If this is undermining the level of trust that general people have in the United States, then that would be the biggest fallout — a loss of soft power, a loss of attractiveness as a player and a partner. It's more a mass effect of the grass-roots level more than fallout at the highest level."

The grass roots may be pushing their leaders into a more forceful response. And because these leaders are already so unpopular for using austerity measures to stanch the eurozone fiscal crises, the surveillance issues may have unexpectedly durable diplomatic impact. This is just one more reason why a necessary national debate over U.S. government surveillance needs to take place. Failure to do so risks alienating allies at a time when trust is essential for a cohesive counterterrorism strategy, let alone inking and implementing a transatlantic trade pact.

"The lessons learned on the American side is that once this kind of surveillance and spying reaches a certain kind of proportion, then it can become detrimental," said Techau. "Then the fringe benefit of doing it, as opposed to what you are actually losing by doing it — then the calculation can all of a sudden change. Because you can lose a lot of confidence that the United States is actually doing the right thing. And that is a very high price to pay."

John Rash is a Star Tribune editorial writer and columnist. The Rash Report can be heard at 7:50 a.m. weekdays on WCCO Radio, 830-AM. On Twitter: @rashreport.