The crisis in Ukraine is just the type of situation in which the U.S. intelligence community might once have monitored Merkel's private phone conversations for insights beyond what she might share directly with Obama.
Merkel, a key European leader, expressed outrage when documents provided by National Security Agency leaker Edward Snowden revealed the U.S. was monitoring her cellphone conversations, as well as those of 35 other foreign leaders. In the ensuing diplomatic to-do, Obama promised Merkel that the U.S. would stop listening to her calls.
Spying on allies is a tricky proposition: It hurts diplomatic relations when one ally discovers that another is spying. But it can help diplomacy when policy-makers have an inside look at what a key foreign leader and the allies she speaks with are thinking on a specific issue.
As the U.S. and its allies try to step up pressure on Russian President Vladimir Putin, a key question is how tough European sanctions against Moscow will be. And that depends largely on what Germany supports. Germany is the world's largest importer of Russian natural gas, so sanctions that damage Russia's economy also could hurt Germany. Obama is meeting with key European allies, including Merkel, in Brussels on Wednesday as part of his weeklong trip to Europe.
Merkel has sent mixed messages about how to respond to Russia annexing the Crimean Peninsula from Ukraine.
She has repeatedly called for a diplomatic solution to the dispute and proposed a "contact group'' to mediate between Russia and Ukraine. But she has also said Russia's takeover of Crimea violates international law, suggesting the Germans may be willing to take stronger steps.
"To understand her position would be of great value,'' former NSA and CIA director Michael Hayden said.
After all, this type of surveillance is one of the reasons the NSA was created.
"You want to know the innermost thoughts of people in important positions whose decisions really do affect international development,'' Hayden said.
The White House would not discuss whether the U.S. has a clear understanding of Merkel's intentions regarding Russia.
But CIA Director John Brennan highlighted the U.S. intelligence community's role in diplomatic negotiations last week.
Around the globe, he said, future events like those in Ukraine "are shaped by numerous variables and yet-to-happen developments as well as leadership considerations and decisions,'' Brennan said. ``While we do not have a crystal ball, it is our responsibility to identify those variables and considerations and point to the key drivers that will ultimately determine future events.''
The term of art in the intelligence community is "leadership intention'' _ using surveillance to find out what foreign leaders are thinking.
The snooping on allies' conversations didn't go over well with any of the world leaders Snowden showed the U.S. was spying on, but it particularly stung Merkel, who grew up in the former East Germany, where eavesdropping by secret police was rampant during the Cold War.
Soon, U.S. intelligence collection was not just a political problem for Obama domestically, it became a diplomatic liability and forced the White House to make a judgment call.
"Is the intelligence value that we would get greater than the risk of having a political blow-up with an ally'' said Michael Allen, a former member of the National Security Council, the White House body that typically weighs such policy decisions. Allen, now managing director at Beacon Global Strategies, a national security consulting firm, said that's a decision that has to be made on a case-by-case basis.
One of the panels tasked with reviewing U.S. surveillance operations came to the same conclusion last year and suggested a new process for "high-level'' approval of sensitive intelligence collection, like spying on U.S. allies.
For now, though, Obama has said the U.S. won't spy on Merkel anymore. And he's reined in the surveillance of dozens of other foreign leaders.
"I've made clear to the intelligence community that unless there is a compelling national security purpose, we will not monitor the communications of heads of state and government of our close friends and allies,'' Obama said in January.
Obama has said the situation in Crimea is a national security concern for the Ukraine and Europe. But the White House would not say whether Crimea meets the threshold for spying on foreign allies.