US Silent As Turkey Starts Receiving Russian S

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.

Turkey "will face very real and negative consequences if it proceeds," the Department of State previously warned.

Read more: Turkey says the first parts of its Russian-made S-400 started arriving Friday, and the US says it will respond

The US has already restricted Turkey's participation in the F-35 program, canceling training and halting the planned delivery of the fifth-generation fighters.

The US has consistently stressed that the stealth fighters are incompatible with the Russian system. Officials are concerned the Russian S-400 could be used to gather information on the US fighter, potentially weakening the aircraft by exposing its stealth capabilities.

The US has pushed Turkey to buy the Patriot instead of the S-400.

Read More: Here's how Turkey's plans to buy Russia's S-400 missile-defense system could expose the F-35's advanced tech

"We are aware of Turkey taking delivery of the S-400," Acting Secretary of Defense Mark Esper said Friday morning. "Our position regarding the F-35 has not changed." He met with his Turkish counterpart later in the day.

The Pentagon canceled a briefing where it was expected to announce a response to the latest developments. The White House and State have been equally silent.

Turkey's decision to acquire the S-400 threatens to erode the NATO alliance, which many observers suspect is Moscow's end goal.

A spike in tensions between the US and Turkey could call into question the future of US deterrence assets stored in country, specifically the nuclear weapons at Incirlik air base, as well as F-35 production processes that are completed in Turkey.

The US has found itself at odds with Turkey before, but this situation is not without new challenges.

"Turkey has taken an action that militarily undermines NATO allies," Jim Townsend, a NATO expert, told Business Insider.

While there have been political divisions within the alliance, this is an apparent first. In that respect, the US and its ally are sailing into uncharted waters.

"They're playing chicken at 200 mph, just waiting to see who swerves first," Townsend said.

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