Ignoring demonstrators in the hearing room and frustrated Senators on the committee dais, CIA nominee John Brennan used a hearing to strongly defend Obama Administration plans to use drones to target Americans overseas who are linked to Al Qaeda.

"I think the American people would be quite pleased to know that we've been very disciplined, very judicious, and that we only use these capabilities as a last resort," Brennan said in testimony to the Senate Intelligence Committee.

Despite tough questions on drones, interrogation policy and more, Brennan seemed to emerge from the hearing all but assured of confirmation to the post; he started his intelligence career 25 years ago as a CIA analyst.

"The CIA's mission is as important to our nation's security today as at any time in our nation's history," Brennan told Senators.

Brennan's testimony came amid building controversy as Senators were still digesting the legal rationale behind the President's decision to target Americans overseas, if they were linked to Al Qaeda.

The revelations particularly left Democrats on the panel frustrated, not only over being left out of the loop on the tactic, but also opposed to the policy itself.

"It's the idea of giving any President unfettered power to kill an American without checks and balances that's so troubling," said Sen. Ron Wyden (D-OR).

Other Democrats were also left frustrated by the lack of information and the direction of U.S. anti-terror policy, which many thought would not push new boundaries after the Bush Administration.

"It is vitallly important for Congress and the American public to have a full understanding of how the executive branch interprets the limits and boundaries of this authority," wrote a group of Senators to the President.

"Everyone – not just select members of Congress – has a right to know when the government believes it can kill American citizens," said Chris Anders of the American Civil Liberties Union, which called on the White House to release more information about the targeting of Americans overseas.

While Democrats were wringing their hands about the drone issue, Republicans left it alone, questioning Brennan sharply about intelligence leaks from the White House, which he denied any role, saying he is a witness, not a subject in the ongoing Justice Department investigation.