Thursday April 4, 2019US VP Mike Pence describes the Russian-Turkish deal as 'deeply troubling' and says it 'poses great danger to NATO'.Turkey hopes to convince the US that the Russian S-400 surface to air missile system will not be a risk or threat to NATO [Vitaly Nevar/Reuters]US Vice President Mike Pence warned Turkey on Wednesday that it could risk its membership in NATO if it goes ahead with plans to buy a Russian air defence system despite widespread international opposition.