U.S. Senator Lindsey Graham, a close ally of President Donald Trump, said this week he was trying to get Turkey readmitted into the programme to help build and operate F-35 advanced fighter jets after it was suspended for buying Russian S-400 air defence missiles.

Graham has also strongly argued against taking measures against Turkey under the Countering America’s Adversaries Through Sanctions Act (CAATSA), which obliges the U.S. administration to punish any country that makes a significant purchase of military hardware from Russia.

But Trump has so far held back from implementing CAATSA measures against Turkey and Graham’s comments could indicate a move within the administration to lift the suspension from the F-35 programme imposed in July after the first S-400 parts were delivered to Ankara.

“We’re trying to get them back in the F-35 programme,” Graham said following a meeting with Turkish President Recep Tayyip Erdoğan on September 22.

On Friday, Turkish Foreign Minister Mevlüt Çavuşoğlu claimed that Washington is currently considering letting Turkey back into the program.

Graham argued in July that if Turkey did not activate the S-400s, then it should not be subject to sanctions.

But U.S. Defense Secretary Mark Esper insisted in August that Turkey had to completely remove the S-400s before the United States would even consider readmitting it to the F-35 programme.

Trump is frustrated that the United States cannot sell Turkey the 100 F-35s it has ordered, calling it “not fair.”

Max Hoffman, associate director of national security and international policy at the Center for American Progress Action Fund, said he suspected Graham was exploring the possibility of Turkey’s readmission to the F-35 programme with Trump’s tacit approval.

But, he said, “the professional ranks of the U.S. government and most of Congress remain unified in their opposition to readmitting Turkey to the programme without the removal of the S-400s”.

Turkey’s permanent removal from the F-35 programme would result in it losing an estimated $9 billion worth of contracts to build some 1,000 parts for the aircraft, ranging from cockpit displays to landing gears and fuselage parts.

Nicholas Danforth, a senior visiting fellow at the German Marshall Fund, distinguished between the prospect of Turkey facing CAATSA sanctions and its suspension from the F-35 programme, which was because of fears Russia could use the S-400s to gather information on the jets’ defences.

“While CAATSA is a political matter, the decision to remove Turkey from the F-35 programme was the result of concrete concerns about the plane’s security,” Danforth said. “This means that short of Erdoğan shipping the S-400s back to Russia tomorrow, it’s very hard to see how Turkey would be readmitted to the programme in the near future.”

Aaron Stein, director of the Middle East programme at the Foreign Policy Research Institute, said that the F-35 talk “has just gotten to be an absurdity”.

“Turkey is being removed from the programme, Turkey will be replaced,” Stein said. “Lindsey Graham is trying to get Ankara to undo the S-400 purchase in exchange for a free trade deal and F-35s … I’ve got news for Lindsey, there won’t be a free trade deal. He isn’t the first to try this. So this back and forth is just tiresome.”

Ali Demirdas, professor of international relations and contributor to The National Interest, said that while Congress wanted to implement CAATSA sanctions on Turkey when it received the S-400s, it opted not to after Turkey threatened a military operation against U.S.-backed Kurdish forces in northern Syria.

“The U.S. has been offering all sorts of incentives to Turkey to prevent an incursion, such as increasing the trade volume to $100 billion, and easing up tariffs on steel and aluminium,” Demirdas said. Graham’s effort to try to get Turkey back into the F-35 programme was “part of this effort to disincentivise a Turkish military operation”, he said.

Demirdas pointed out that Turkish companies were completing existing orders for F-35 components and its participation in making parts of the jets would not end until next March.

U.S. sources said removing Turkey from the programme would not be as costly and complicated as the Turkish government says, as other countries could step in and make the parts.

Demirdas said the F-35s already suffered from a lack of spare parts. A study by the Government Accountability Office said that between May and November 2018 only 27 percent of all F-35s were fully mission capable, while 52 percent were mission capable. This, it said, was largely due to a shortage of spare parts and “difficulty managing and moving parts around the world”.

“Considering that Turkey committed to buying 100 F-35s, it would be dumb to bump Turkey out of the programme, given the already bleak future forecast of the programme,” Demirdas said. “So, I am of the opinion that Turkey will somehow remain in the programme and will receive its F-35s if Trump gets re-elected, regardless of the S-400 situation.”

But Stein said the F-35 spare parts issues were not Turkey-related and would be addressed as the programme matured. He said Turkey had many options for air and missile defence, but chose the Russian one. “It chose S-400 knowing that it would lose F-35,” Stein said.

Anticipating that it would not take delivery of F-35s, Turkey stockpiled spare parts for its large F-16 fleet, which the F-35s were supposed to replace.

Demirdas said despite Russian-backed attacks on Turkish-backed rebels in Syria’s Idlib province, Russia was doing more to appease Turkey’s security concerns in Syria compared to the United States, which was supporting the Syrian Kurds.

“Therefore, I don’t expect that Turkey will hurt its relations with Russia,” he said. “This being said, the U.S. should do more for Turkey than what Russia is doing to pull Turkey away from Russia’s strong orbit.”

That would require major U.S. concessions on its support for Syrian Kurdish forces and its refusal to extradite Fethullah Gülen, the man Turkey says was behind the 2016 coup attempt, Demirdas said.

“It appears now that the U.S. needs Turkey more than Turkey needs the US,” he said. “Therefore, it is very unlikely that Turkey will deactivate the S-400 systems.”

Hoffman also doubted Erdoğan would give up on the S-400 deal at this late stage, “having incurred such a large cost in both material and political terms, and even despite Russia continuing its campaign in Idlib against Turkish wishes”.

While Trump might want to allow Turkey back into the F-35 programme “unified Congressional and executive interagency opposition to such a move will likely preclude it”, Hoffman said.