As President Barack Obama's pick for CIA director heads to Capitol Hill for his confirmation hearing Thursday, some in the president's own party are threatening to hold up John Brennan's nomination.

Oregon Democratic Sen. Ron Wyden told reporters he would "pull out all the stops" to get answers about the legality of targeting Americans involved with al Qaeda overseas. Wyden was not satisfied with a confidential Justice Department memo that was sent to key congressional committees last year but only became public on Tuesday.