Illustration by Oliver Munday for TIME

Nearly a century ago, long before the National Security Agency existed, there was the Black Chamber. Founded after World War I, the New York City–based office — formally called the Cipher Bureau and disguised as a commercial company — existed to crack the communications codes of foreign governments. The bureau closed in 1929, a decision Secretary of State Henry Stimson later justified with the quaint declaration: “Gentlemen do not read each other’s mail.”

More than 80 years later, that warning is haunting President Obama. New revelations from fugitive NSA leaker Edward Snowden have exposed extensive U.S. surveillance on overseas allies, including a program that targeted 35 foreign leaders, even tapping German Chancellor Angela Merkel’s cellphone. Not very gentlemanly at all.

That has fueled a push in Congress to rein in the NSA. An infuriated Dianne Feinstein, the Democratic Senate Intelligence Committee chairwoman — often a defender of the NSA — announced “a major review” of all U.S. intelligence operations. “The reports are very disturbing,” Republican Senator Susan Collins told ABC News. “Friends don’t spy on friends.”

(MORE: NSA Defender Feinstein Blasts Spying on Allies)

Yes, they do. The latest NSA flap may be less a story about a spy agency run amok than a peek into a world where for political leaders, the walls (and phones, tablets and laptops) always have ears. “All big countries use espionage, and some of the countries that are complaining spy on the U.S.,” says James Andrew Lewis, a former American diplomat now at the Center for Strategic and International Studies. It’s not that countries think their friends are plotting against them; their aim is to gain insights into coming policy shifts or learn tidbits about third-party rivals.

Consider the now forgotten story of Echelon. In 2000, European leaders raged at reports that the U.S. was covertly gathering data on the continent’s economic activity. A report commissioned by the European Parliament condemned the U.S.’s activities. But in the game of foreign surveillance, there are few clean hands. In 2004 a former British Cabinet minister alleged that U.K. agents had bugged the office of U.N. Secretary-General Kofi Annan. An official document leaked to a British newspaper in 2009 showed that the U.K. was a high-priority espionage target for 20 countries — including chums like France and Germany.

America too is a routine target of its allies. At a 2009 NATO summit in France, Obama’s aides ditched their BlackBerrys, presumably for fear of eavesdropping. In 2010, National Intelligence Director Dennis Blair proposed an espionage cease-fire with the nosy French on the grounds that the two countries were wasting valuable counterintelligence assets dueling each other that were better applied to nations like China and Russia. (The White House shot down the idea.)

(MORE: NSA Official: NATO Allies Helped Collect European Phone Records)

After French officials railed at a report that the NSA had scooped up millions of phone-call records from their country, France’s former top intelligence official Bernard Squarcini scolded them. “I am amazed by such disconcerting naiveté,” Squarcini told Le Figaro. “The French intelligence services know full well that all countries, whether or not they are allies in the fight against terrorism, spy on each other all the time.” (Further muddying the morality, U.S. officials insist that France and Spain collected the data themselves and passed it along to the NSA.)

The bugging of foreign leaders has had particular power because it seems so personal. Obama has befriended Merkel, for example, so the snooping on her cellphone carries a whiff of betrayal. Which is why Obama is reportedly weighing a ban on tapping friendly heads of state.

Intelligence insiders say that would amount to unilateral disarmament by the U.S. “Let’s be honest — we eavesdrop too. Everyone is listening to everyone else,” former French Foreign Minister Bernard Kouchner told France Info radio. If the NSA earns special scorn, he added, it’s because “we don’t have the same means as the United States — which makes us jealous.”

MORE: An Angry Europe Faces Up to U.S. Spying and the War on Terrorism’s Legacy