Although John Brennan is very likely to be confirmed as the United States' head of the Central Intelligence Agency (CIA), it's expected that he will face some tough questions during his Senate hearing. Some politicians are worried about any role he might have potentially played in the leaking of national security information as well as the CIA's post-9/11 torture program. Today, however, comes news that he might also field some uncomfortable queries about drone strikes.

The invention of the unmanned drone was a huge technological event for the United States, opening up new ways to fight the war on terror while also leaving numerous legal questions on the table. Notably: Can the President decide to kill an American citizen without a trial? How is that decision made?

So far, the Obama administration has refused to release any information regarding its decision-making process, claiming it is classified information. Ahead of Brennan's hearing, however, Democratic Senator Ron Wyden is trying to bring up the issue again in a letter he wrote to the CIA nominee.

"For the executive branch to claim that intelligence agencies have the authority to knowingly kill American citizens but refuse to provide Congress with any and all legal opinions that explain the executive branch's understanding of this authority represents an alarming and indefensible assertion of executive prerogative," wrote Wyden.

Wyden claims that he has asked the administration multiple times for information regarding the targeted killing of Americans only to be rebuffed each time. He asks Brennan explicitly for a list of countries in which the Obama administration authorized the use of lethal force. Additionally, Wyden wants to know how the administration decides when it becomes impossible to bring in alive an American suspected of terrorism.

Though Wyden is not necessarily opposed to Brennan's nomination to the CIA, he wants the government to be a lot more forthcoming with details to ensure the appropriate checks and laws are in place, and that targeted killings are implemented properly.

At the end of the letter, Wyden asks a number of pointed questions:

"How much evidence does the President need to determine that a particular American can be lawfully killed?"

"Does the President have to provide individual Americans the opportunity to surrender before killing them?"

"Do any intelligence agencies have the authority to carry out lethal operations inside the United States?"

The Senate Intelligence Committee is expected to hold Brennan's confirmation hearing on Feb. 7.