The White House on Tuesday defended targeted assassinations of Americans thought to consort overseas with terrorists as “necessary,” “ethical” and “wise,” as the Obama administration faced fresh questions about its sharply expanded drone war.

"We conduct those strikes because they are necessary to mitigate ongoing actual threats—to stop plots, prevent future attacks and, again, save American lives,” White House press secretary Jay Carney told reporters. “These strikes are legal, they are ethical, and they are wise."

Carney’s comments came after NBC News published a Justice Department memo that lays out a broad rationale for targeting individual Americans anywhere outside the U.S. for assassination—without oversight from Congress or the courts, and even if the U.S. citizen in question is not actively plotting a specific terrorist attack.

The 16-page document, obtained by NBC News, emerged days before John Brennan, Obama's chief counterterrorism adviser and the foremost architect of America’s hugely controversial unmanned aerial vehicle war, goes before the Senate Intelligence Committee in a Thursday hearing on his confirmation as CIA director.

Obama campaigned in 2008 as a fierce critic of George W. Bush’s national security policies, notably interrogation practices widely seen as torture. He also left little doubt that he would order unilateral strikes inside another country if he deemed them necessary. In office, he has apparently learned to stop worrying and love executive power—the literal power of life and death over fellow U.S. citizens overseas when he suspects they are consorting with extremists groups that may be targeting America. So, under what circumstances does he have the right to act?

The memo says “an informed, high-level official of the U.S. government” must decide that the target is a "senior operational leader" of al-Qaida or "associated forces"; “poses an imminent threat of violent attack against the United States”; and that an attempt to capture that individual is “infeasible.”

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“Targeting a member of an enemy force who poses an imminent threat of violent attack to the United States is not unlawful. It is a lawful act of self-defense,” the document asserts.

"Imminent threat"? That seems reasonable and is a traditional standard for military action. Except, as NBC investigative reporter Michael Isikoff notes, the memo adds that “the condition that an operational leader present an ‘imminent’ threat of violent attack against the United States does not require the United States to have clear evidence that a specific attack on U.S. persons and interests will take place in the immediate future.”

Instead, that previously mentioned "high-level official" can determine that the potential target was “recently” involved in “activities” posing a threat of an attack and that “there is no evidence suggesting that he has renounced or abandoned such activities.”

Isikoff notes the memo does not define "activities" or "recently," leaving that up to the administration to determine on a case-by-case basis.

A reporter asked Carney about the case of Abdulrahman al-Awlaki, the teenage son of Anwar al-Awlaki, an al-Qaida supporter killed by a U.S. drone in Yemen. The boy, 16, was killed in another drone strike about two weeks after his father. Was the son a “senior operational leader” of a terrorist group, a reporter asked. That seemed to stump Carney. “I’m not going to talk about individual operations that may or may not have occurred.”

But Obama wages this 21st-century war in a manner “consistent with the Constitution and our laws,” while aides review the difficult legal and ethical questions “with great care and deliberation,” Carney said.

The memo notes that the president can order a strike against al-Qaida far beyond the battlefield of Afghanistan, and it makes clear that he will not be constrained by national sovereignty. Either a country will give the green light to drone strikes on its territory, or America will strike if that country is "unable or willing" to do so.

This is no surprise. Obama famously said in the 2008 campaign that he would order an attack inside Pakistan to get Osama bin Laden, whether or not Islamabad signed off. He made good on that promise, ordering the raid on bin Laden's compound in Abbottabad, Pakistan, on May 1, 2011, which killed the terrorist leader.

The memo is sure to trigger another round of questions from Congress about the drone war, which has been shrouded in secrecy. And it comes at a time when that campaign is powerfully unpopular overseas, according to a June 2012 Pew Research poll. While 62 percent of Americans approve of the approach, 44 percent of respondents in staunch ally Britain do. And the numbers plummet in countries with large Muslim populations: 6 percent in Egypt, for instance, and 9 percent in NATO ally Turkey.

That's in part the reflection of anger over civilian casualties from such attacks. Obama has grappled with that problem ever since the very first drone strike on his watch, a Jan. 23, 2009, attack that reportedly claimed the life of "an innocent tribal elder" in Pakistan. A May 2012 New York Times report said the administration minimizes civilian casualties by counting "all military-age males in a strike zone as combatants."

The memo drew a withering response from the American Civil Liberties Union.

“This is a profoundly disturbing document, and it’s hard to believe that it was produced in a democracy built on a system of checks and balances,” said Hina Shamsi, director of the ACLU’s National Security Project. “It summarizes in cold legal terms a stunning overreach of executive authority—the claimed power to declare Americans a threat and kill them far from a recognized battlefield and without any judicial involvement before or after the fact.”