Judge Andrew Napolitano weighed in on "The O'Reilly Factor" last night on the legality of killing traitors to America.

The discussion focused on the killing of Anwar al-Awlaki, an al Qaeda operative and U.S. citizen who was killed in a CIA drone strike in Yemen in 2011.

The terrorists who attacked Charlie Hebdo in Paris last week are said to have past ties to al-Awlaki.

The strike on a U.S. citizen has raised constitutional questions, with the judge arguing in the past that no president can claim the power to kill an American citizen.

O'Reilly began the discussion by pointing out that in previous wars, enemy collaborators were killed by American forces on the battlefield.

"Why are you complaining about this?" he asked.

Napolitano said those previous examples literally involve deserters on the battlefield, but American citizens - even those accused of joining al Qaeda - are afforded protections by the Constitution.

"It's not my beef, Bill O'Reilly. It's the Constitution's beef," the judge said, arguing "if they can do it to al-Awlaki, they can do it to anybody."

O'Reilly accused Napolitano of "hiding behind" that argument, saying Congress approved these actions after 9/11 and only one American has been killed in this manner.

Napolitano pushed back, saying Congress "never authorized the president to kill people who haven't been charged with a crime."

O'Reilly argued that Napolitano was "misusing" the Constitution to make his argument, while the judge countered that O'Reilly was "totally misreading" the powers granted to the president by Congress.

O'Reilly called the judge's beliefs on the issue "dangerous" and said they would "tie up" the people trying to protect the country from jihadists.

Watch the rest of the spirited debate above.