The admission by Director of National Intelligence Dennis Blair that the United States intelligence community is authorized to assassinate Americans working with terrorists overseas has raised serious questions of constitutionality.

"It's troubling, Keith, because it's not on the books," constitutional law professor Jonathan Turley told MSNBC's Keith Olbermann on Thursday.

"This is something that President Bush developed," Turley explained. "We actually saw the Bush administration kill an American citizen named Kamal Derwish in 2002 with a Predator strike. ... The Obama administration, once again, seems to be morphing into the Bush administration."

According to investigative reporter Seymour Hersh, the American officials who directed the strike that killed Derwish in 2002 were not aware that he was in the targeted car. In contrast, the attempt to take out al Qaeda operative Anwar al Awlaki last December with a cruise missile directly targeted the America-born cleric.

"The problem is that there's a term for this," Turley went on. "It's called assassination. You're taking out someone, a US citizen, who's had no chance to prove that they're innocent. ... US citizens are entitled to trials."

"It doesn't say you can't kill a US citizen who's engaged in a terrorist act," Turley cautioned. "But to use this term of 'involved' in an organization raises some very troubling legal and constitutional issues."