WASHINGTON: In what could be a grim foreboding for New Delhi and Indo-US ties , the Trump administration announced on Friday that it would stop training Turkish pilots on F-35 stealth fighters and cancel the sale of the jet to Turkey if the country went ahead with buying the Russian S-400 air defence system — a purchase India has also committed to in the face of Washington’s opposition.The Pentagon went so far as to ask 42 Turkish pilots — who have been training in Arizona and Florida for the past several months preparing to receive the first of 100 F-35s Turkey has contracted to buy – to leave the United States by July 31.The Pentagon also said it would end Turkish participation in management and manufacturing activities related to the F-35 program. Turkish companies are said to currently produce almost 1,000 parts for the F-35, including landing gear and fuselage components."While we seek to maintain our valued relationship, Turkey will not receive the F-35 if Turkey takes delivery of the S-400," Acting US defence secretary Patrick Shanahan wrote in a blunt letter to his Turkish counterpart Hulusi Akar. "You still have the option to change course on the S-400."The US is arguing that putting the S-400 system in proximity to the F-35, America’s most advanced fighter, would allow Russia to learn too much about the aircraft’s radar profile and potential vulnerabilities.Washington has made similar arguments to India, implicitly warning that buying the Russian S-400 will cast a shadow on the burgeoning US-India ties that has seen big Indian purchase of American arms.A squeeze on Turkey could devolve into a test case of New Delhi's heft and spine, how substantial and important a partner India is to the United States, and whether the American pursuit of a new Indo-Pacific policy to counter China will allow Washington and New Delhi some wiggle room on the S-400 issue.The tough-talking Trump administration is indicating that it will not hesitate to throw Turkey, a Nato ally, under the bus if its commercial and strategic interests are affected.The Russian purchase "will hinder your nation’s ability to enhance or maintain cooperation with the United States and within NATO, lead to Turkish strategic and economic over-dependence on Russia, and undermine Turkey’s very capable defence industry and ambitious economic development goals," Shanahan warned in his letter leaked to the US media.Although India is not a NATO ally, is less militarily dependent on Washington, and does not manufacture any arms systems or subsystems for the US, it has nevertheless developed close military ties with the US Washington has been trying hard of hawk a souped-up F-16, dressed up as an India-specific F-21 with some F-35 features. New Delhi is not biting.Like India, Turkey has also argued that it has already gone too far with its commitment to buy the Russian system and it is a done deal. It has also said the US counter offer to sell its Patriot missile defence system – something American officials have also implied could be available for India if it ditches the S-400 – is too late and too expensive.The Trump administration has sent it assistant secretary of state for politico-military affairs R Clarke Cooper to New Delhi this week to make the case for the F-16/F-20 and against the S-400 in the backdrop of the larger security relationship.Ahead of the visit, a fact sheet issued by the politico-military bureau said India is the first non-treaty partner to be offered a MTCR Category-1 Unmanned Aerial System (Drone) – the Sea Guardian UAS manufactured by General Atomics. It said the administration also "continues to support advocacy for the Lockheed Martin F-21 and Boeing F/A-18 – two state of the art fighter aircraft that India is currently evaluating," suggesting the US is still hoping to wean India away from further European and Russian purchases."These platforms provide critical opportunities to enhance India’s military capabilities and protect shared security interests in the Indo-Pacific region," it added.Section of the Turkish media speculated though that Washington’s actions were part of the pressure tactics by the Trump administration before President Trump meet’s Turkey’s President Erdogan at the G-20 summit in Osaka later this month.Prime Minister Modi will also be there and is expected to meet Trump. They will likely be talking Turkey – at least idiomatically.