The United States government employs lethal drone strikes only as a last resort to prevent terrorist attacks and only with the utmost care, the president’s nominee to head the Central Intelligence Agency told Congress on Thursday.

John O. Brennan attempted a charm offensive on behalf of the cloak-and-dagger agency, vowing in his confirmation hearing to be more forthcoming with the public and legislators about CIA actions.

He faced a tough crowd, including skeptical, detailed questioning from Georgia U.S. Sen. Saxby Chambliss, the leading Republican on the Intelligence Committee.

“Your view seems to be that even if we can save American lives by detaining more terrorists using only traditional techniques, it would be better to kill them with a drone rather than detain them,” Chambliss said.

Brennan disputed that, saying the first choice always is to detain. But Chambliss, who will help shape how Brennan’s confirmation proceeds, pointed out that the Obama administration has detained only one “high-value” suspect in four years — opting far more often to assassinate enemies.

At the start of the hearing Brennan was interrupted repeatedly by protesters who appeared to be affiliated with the anti-war group Code Pink. One waved a child’s doll, asking the committee chairman, U.S. Sen. Dianne Feinstein, a California Democrat, if her children were more important than those in Pakistan and Yemen who died in drone strikes.

After the fifth interruption, Feinstein cleared the room except for senators, staff, VIPs and news media. The agitators and the rest of the public could follow along on C-SPAN.

Later, Brennan said, “The people that were standing up here today, I think they really have a misunderstanding of what we do as a government and the care that we take, and the agony that we go through to make sure that we do not have any collateral injuries or deaths.”

Brennan spent 25 years at the CIA, including major roles during the George W. Bush administration. He retired from the agency and then worked on Barack Obama’s presidential campaign in 2008. In the White House he has served as a top counterterrorism adviser.

Senators repeatedly pressed Brennan for assurances that he would be more forthcoming with the classified details of CIA actions so the committee can oversee the agency.

Facing criticism ahead of Brennan’s confirmation hearing, Obama this week gave Congress the internal legal memos — including classified documents — that justify drone strikes.

“Every American has the right to know when their government believes it’s allowed to kill them,” said U.S. Sen. Ron Wyden, an Oregon Democrat. “Ensuring that the Congress has the documents and information it needs to conduct robust oversight is central to our democracy.”

Feinstein said that she wanted the CIA to be more transparent in order to protect itself. She bemoaned that she cannot say exactly how many civilians have been killed in drone strikes because it is classified, but she said it “has typically been in the single digits” annually.

The most controversial drone strikes under discussion were ones that killed American citizens, including al-Qaida figure Anwar al-Awlaki and his 16-year-old son. They were killed in Yemen. Feinstein asked for more detail from Brennan on al-Awlaki’s ties to terror plots against Americans in order to demonstrate to the public the necessity of killing him.

Several senators pressed Brennan on interrogation policy. He said he believes simulated drowning, known as “waterboarding,” is wrong. But he declined to comment on whether it was torture, explaining, “I’m not a lawyer.” He also said he is unsure if waterboarding ever yielded effective intelligence.

Chambliss expressed doubt that this was always Brennan’s view, noting that Brennan never did anything to stop waterboarding while in the CIA. Brennan said he made his concerns known to colleagues but had no control over the program, which was run out of a different part of the agency.

Wyden has said unless the administration gives him more legal documentation about drone strikes he will filibuster Brennan’s nomination — meaning Brennan would need 60 Senate votes rather than 51 to be confirmed. But a rejection of such a nominee is exceedingly rare.

“There are probably as many Democrats that are not happy with him right now as are Republicans,” Chambliss said in a Fox News interview after the hearing.

The committee will have a classified chat with Brennan behind closed doors next week, and Chambliss said one of his primary concerns is whether Brennan shifted his views on waterboarding because of the political winds. “We’re going to have to probe that a little more,” he said.