…Turkey still has Russian S-400 air defense missile systems?

The Trump administration is expected to override a decision by a Democratic lawmaker who is blocking a proposed $750 million sale of jet engines to Turkey over concerns about the country’s ties to Russia.
Congressman Gregory Meeks (D, NY) had placed a hold on the sale to Turkey—a NATO ally that is hosting an alliance summit next month—because the country continues to hold a Russian S-400 air-defense system that it bought roughly a decade ago, along with other concerns about Turkey’s role in the region.

That S-400 system, after all, might spy on Turkey’s F-35s and learn how to defeat it.

This is silly. There are reasons to not sell F-35s to Turkey, but the idea that the S-400 can compromise the F-35’s stealth capabilities isn’t one of them, at least not anymore (if it ever was). We’ve sold lots of F-35s to other nations over the years. If the jet’s stealth capabilities could ever be compromised, they already have been, just from their use around the world and our enemies observing their use, including by those objectionable S-400 systems, and collecting data on detecting and otherwise countering the jets. And that foolishly ignores the fact that over those intervening years of F-35 operational use, there have been a plethora of—steadily more and more capable—systems watching and observing and analyzing the F-35 in all its operational flexes.

There are reasons for going ahead with the sale, too, and these should be weighed against those reasons for not selling. The presence of S-400s in the buying nation is not relevant.