The heightened focus on President Obama's targeted killings of American terror suspects overseas has rattled members of his progressive base who have stayed mostly silent during an unprecedented use of secret drone strikes in recent years.
During the presidency of George W. Bush, Democrats, including then-Sen. Obama, hammered the administration for employing enhanced interrogation techniques, which critics labeled torture.
Liberals have hardly championed the president's drone campaign but have done little to force changes in the practice, even as the White House touts the growing number al Qaeda casualties in the covert war.
The issue grates on some Democrats who backed Obama over Hillary Clinton because of her vote in favor of the war in Iraq, only to see the president ignore a campaign promise to close the detainee holding camp in Guantanamo, Cuba, and mount a troop surge in Afghanistan.
With the confirmation hearing Thursday for John Brennan, Obama's nominee for CIA director -- and the architect of the drone program -- Democrats will have a high-profile opportunity to air their concerns over the controversial killings.
"You watch and see -- the left wing of the party will start targeting Obama over this," said Larry Sabato, a political scientist at the University of Virginia. "It's inevitable. The drumbeat will increase as time goes on, especially with each passing drone strike."
Obama late Wednesday decided to share with Congress' intelligence committees the government's legal reasoning for conducting drones strikes against suspected American terrorists abroad, the Associated Press reported. Lawmakers have long demanded to see the full document, accusing the Obama administration of stonewalling oversight efforts.
Earlier in the day, one Democrat even hinted at a possible filibuster of Brennan if given unsatisfactory answers about the drone program