(CNN) -- It may not be as gripping as a spy novel, but things are heating up after the latest reports of espionage by the U.S. National Security Agency.
International leaders say they're outraged, and the Obama administration says it's investigating.
Here are five key questions to keep in mind:
1. Are U.S. President Barack Obama's hands clean in this?
It's not really clear.
The Wall Street Journal reported that an internal review of U.S. surveillance programs that started this summer revealed the NSA had tapped the phones of about 35 world leaders and that the White House ordered a halt to some of it.
That would suggest the President did not know about the programs for the nearly five years he has been in office.
The White House says the President did not know specifically about the tapping of German Chancellor Angela Merkel's phone, but hasn't said anything about what he knew regarding spying on any other world leaders.
2. What does it say about Obama as a leader if he didn't know?
Officials say it's understandable that Obama wouldn't know about specific wiretapping of leaders because the NSA has so many surveillance programs and he would not be briefed on all of them.
But if, as reported, some of the programs date back to the Bush administration, one would think Obama would have been briefed on this when he took office.
That raises questions about whether Obama knew and is shaving the truth or his own intelligence community kept him in the dark. Neither answer is satisfying.
3. What has Obama done about it?
That's a key question.
In a USA Today op-ed published last week, Obama's homeland security and counterterrorism adviser Lisa Monaco conceded that recent "disclosures have created significant challenges in our relationships." To address them, the President has ordered a "review (of) our surveillance capabilities, including with our foreign partners," she wrote.
As accusations mount and the issue becomes increasingly thorny diplomatically, it's unclear what Obama has said and done behind closed doors.
The Wall Street Journal's report, which cites unidentified U.S. officials, did not specify who gave the shutdown order or the date it was issued.
Germany's Bild am Sonntag newspaper reported Sunday that Obama learned of an operation to monitor Merkel from the head of the NSA and allowed it to continue -- a claim the NSA has denied.
4. Who's upset about this?
The latest spying claims have roiled leaders in Europe and Latin America, who have accused the U.S. government of breaking the law, summoned U.S. diplomats for answers and said their confidence in the United States is shaken.
In Germany, some leaders have suggested tabling discussions of a European Union free trade deal with the United States in response.
In the United States, some have dismissed the foreign leaders' criticism as political bluster, arguing that spying is a common practice in international relations, even for allies.
"These leaders are responding to domestic pressures in their own country. None of them are truly shocked about any of this. ... Everyone spies on everybody. And that's just a fact," U.S. Sen. Marco Rubio, R-Florida, told CNN last week.
A prominent Republican lawmaker told CNN on Sunday that such surveillance programs keep U.S. allies safe.
"If the French citizens knew exactly what that was about, they would be applauding and popping champagne corks," said Rep. Mike Rogers, R-Michigan. "This whole notion that we're going to go after each other on what is really legitimate protection of nation-state interest, I think is disingenuous."
5. What would the U.S. hope to learn by spying on its allies?
The United States says its surveillance programs are for the purpose of foiling terrorist plots, but there are many political reasons for interest in communications of world leaders.
For example, some media reports suggest the tapping of Merkel's phone increased in 2010, around the time of the financial crisis in the Eurozone, in which Merkel was a major player.
The U.S also wants as much information as possible about the actions of other states to make its own decisions about important foreign policy issues, such as Syria and Iran. At the end of the day, allies cannot automatically count on each other's loyalty.
And Washington may use its intelligence to make sure its allies are, in fact, just that.