The US is silent as Turkey starts receiving a Russian missile system that could jeopardize the F-35 stealth fighter

As NATO ally Turkey receives its first shipment of the controversial Russian air defense system that has for months been driving a wedge between Ankara and Washington, the US appears to be struggling to figure out a response in a mounting test for the Trump administration.

On Friday, Russia began delivering the S-400 surface-to-air missile systems Turkey.

"By accepting delivery of the S-400 from Russia, President Erdogan has chosen a perilous partnership with Putin at the expense of Turkey's security, economic prosperity and the integrity of the NATO alliance," the chairmen and ranking members of the Senate Armed Aervices Committee and Senate Foreign Relations Committee said in a statement.

Turkey decided to purchase the advanced system despite strong opposition from the US, which has repeatedly made clear Turkey would face expulsion from the F-35 Joint Strike Fighter program, as well as other possible punitive measures if it did not change course.

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