McCaskill said she was "proud that we have no POWs left in Afghanistan, and the president should be proud also.

"If this man's life was lost and it came out that we had this opportunity and our Commander-in-Chief passed on it, the Republicans would be crazy right now," she told Wallace. "We saved this man's life."

Some historians point out that, depending on how one defines a terrorist, the United States has negotiated with them dating to the beginnings of the republic.

Frank Lambert, a Purdue University historian and author of "The Barbary Wars" and several other books on colonial and early U.S. history, said the U.S. essentially did so during constant conflict with the Barbary states of north Africa.

The Washington and Adams administrations negotiated tributes and ransoms to be paid to "corsairs" - privateers that sailed under the authority of the Barbary states who often captured cargo and sailors of U.S. ships, he said. Thomas Jefferson, tired of paying the tributes, in 1801 declared war. The "shores of Tripoli" line in the Marine Hymn comes from that war.

"Yes, I think the corsairs were terrorists, and, yes, the U.S. did negotiate with them," Lambert wrote in an email Wednesday. "More importantly, Americans at the time thought Washington and Adams, and some included Jefferson, negotiated with terrorists."

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