Can tensions between Turkey and NATO be contained?

Two US senators are demanding sanctions after reports Turkey has tested its Russian-built S-400 defence system.

But 21st century Turkey is a more assertive power.

It has interests in the Middle East and Central Asia – and those may not sit comfortably with its role in NATO.

Last year, NATO expelled Turkey from its programme to build the F-35 fighter jet, designed for use throughout the alliance.