It’s not clear why talks with the UAE may have stalled. One potential reason: The UAE’s possession of the S-400 would prevent it from purchasing its own F-35s.

“I’ve talked to the Emiratis about it, I talked to the Turks about it, but I’m not sure that I got some official position on it,” Sen. Chris Coons, D-Del., said. “I will make a general observation: Any country that purchased the S-400 and deployed it would face the same concerns, challenges, and restrictions … that the Turks did.”

The S-400 isn’t skeptics’ only concern over Türkiye getting access to F-35s, the most advanced fighter jets in use today. Sen. Chris Van Hollen, D-Md., pointed to Ankara’s “crackdown on democracy” as well as its occupation of Cyprus and previous intrusions into Greek airspace.

“I have a long history of being concerned about the sale of the F-35s to Türkiye, apart from any of the current crosscurrents,” Van Hollen said.

Israeli opposition to the F-35 deal is rooted in its pursuit of a regional military advantage, experts say.

“The Israelis have a significant problem with Türkiye acquiring advanced fighter jets such as the F-35 because that would essentially empower the Turkish military, which is already significantly bigger than the Israelis’,” said Sinan Ciddi, Türkiye Program Director at the Foundation for Defense of Democracies.

Israel is pressuring members of Congress to maintain the restrictions on Türkiye’s F-35 acquisition, Ciddi added. Its main lobbying group in DC isn’t hiding its skepticism of the sale.

“We share the concerns raised by some members of Congress about providing the F-35 to a country that welcomes Hamas, helps Iran evade sanctions, and has deepening ties with Russia and China,” AIPAC spokesperson Deryn Sousa told Semafor.

The Iran war has at times strained Trump’s relations with Netanyahu while tightening his ties to Türkiye. That may make it difficult for Israel to prevail in any political standoff in Washington over F-35 sales, whether with Ankara or Riyadh.

“Israel currently has a monopoly on F-35 use in the Middle East, but this will not last forever, as Saudi Arabia will begin taking deliveries by 2029,” Tim Chattell, an international security fellow at Chatham House, said.

Israel’s resistance to the F-35 sale at a time when its standing with Democrats has hit a nadir could also make some in the party reassess their own opposition to it.

“I have my own hesitations about selling F-35s to Türkiye, but I am not interested in advice from Benjamin Netanyahu,” Sen. Elizabeth Warren, D-Mass., told Semafor. She added that his “lobbying here may be having the opposite effect.”

There is still another potential obstacle to an F-35 sale that would materialize if a sale to UAE, or another country, pans out for Türkiye: Moscow. Russia must approve any transfer of the S-400s, giving it unique leverage over a move that it has a significant reason to reject.

The S-400’s continued presence in Türkiye, Ciddi said, “has really sort of undercut the cohesivity of NATO.”