An ex-KGB agent says every American that Putin can imprison is 'an asset that you can trade' as Moscow detains a US ballerina

• Russia's imprisoning of US citizens as bargaining chips is "nothing new," an ex-KGB agent said.
• Jack Barsky told Fox that this gives Moscow an "asset that you can trade."
• Ksenia Karelina, a US-Russian ballerina, is the latest American citizen to be detained by Russia.

Every US citizen detained by Russia gives the Kremlin an "asset that you can trade," ex-KGB agent Jack Barsky said.