Despite the warnings, for Turkey it was already a done deal.
They've bought S-400 air defense systems from Russia, one of the world's most advanced.
They're due to arrive any day now and the U.S. is furious at Turkey's leader, again.
Turkey and the U.S. have sparred publicly for months over Ankara's order.
Turkey is a NATO ally and the fact that the S-400s are not compatible with NATO's systems has raised some eyebrows.
The U.S. State Department warns Ankara will face "real and negative consequences" for the purchase and has threatened sanctions.
So why would Turkey risk upsetting an important NATO ally?
Reuters Turkey Bureau chief Dominic Evans explains.
(SOUNDBITE) (ENGLISH) REUTERS TURKEY BUREAU CHIEF, DOMINIC EVANS, SAYING: "Turkey says when it first reached a deal with Moscow to buy the Russian air defense missile system two years ago there was no alternative on the table from Washington.
By the time the USA.
Came up with another offer, a rival offer for the patriot missile defense system the deal with Russia was done and dusted.
Turkey, although it is a NATO member, a western ally, it has had difficult relations with the United States over the last few years over a number of issues including Syria where Russia is a very powerful player.
So it does make sense on some levels for Turkey to look to alliances elsewhere." Another consequence is losing these stealth fighter jets.
The U.S. could stop Turkish forces from flying and developing its F-35.
Washington has already pulled the plug on training Turkish pilots on the aircraft.
The U.S. and its allies are concerned by installing the system the technology would learn how to recognize the jets.
They're built to avoid tracking by enemy radars and heat sensors.
So, what happens now?
(SOUNDBITE) (ENGLISH) REUTERS TURKEY BUREAU CHIEF, DOMINIC EVANS, SAYING: "Turkey has proposed a working group to look in to the impact of this, of this missile defense system.
It's not got a positive response from Washington on that, so when the S-400's arrive in Turkey sanctions will be imposed on Turkey.
There is a whole range of choices that Washington can pick from in terms of severity of those sanctions but the person who makes the ultimate choice will be President Donald Trump -- which means everybody is still guessing what will happen."