For years, India has carefully balanced its longstanding military and energy relationship with Russia, while steadily deepening its strategic and defence partnership with the United States.That delicate equilibrium enabled New Delhi to strengthen defence, intelligence and technology cooperation with Washington while continuing to rely on Russian weaponry and, more recently, discounted Russian crude oil. But the arrangement was never entirely free of friction.The clearest point of contention emerged over India’s decision to acquire the Russian S-400 ‘Triumf’ air-defence system, prompting President Donald Trump’s first administration to repeatedly warn that the purchase could invite punitive measures under the 2017 Countering America’s Adversaries Through Sanctions Act (CAATSA), enacted specifically to deter major purchases of Russian military equipment and diminish Moscow’s defence exports and geopolitical influence.Yet, those warnings never translated into action. The Biden administration effectively gave India a CAATSA pass, concluding that Delhi’s overall strategic value as a counterweight to an increasingly assertive China outweighed Washington’s continuing unease over its enduring defence relationship with Moscow.Illustration: Pariplab Chakraborty.But that equation may now be changing and, ironically, the clearest indication comes not from Delhi but from Ankara, where Turkey is reportedly trying to rid itself of the very Russian S-400 Triumf air-defence system whose numbers India is preparing to double, in the hope of regaining entry into the US-led F-35 Joint Strike Fighter programme. If confirmed, Ankara’s negotiations would offer a revealing glimpse of where American policy towards countries operating major Russian weapons systems may now be headed.Turkey’s difficulties stem from its US$2.5 billion acquisition in 2017 of two S-400 batteries, the first components of which were delivered in July 2019. The purchase triggered Ankara’s expulsion from the US-led multinational F-35 programme and, a year later, the imposition of CAATSA sanctions. Washington’s objections centred on the risks of operating America’s most advanced stealth fighter alongside Russia’s premier long-range air-defence system, potentially allowing sensitive electronic intelligence on the F-35’s stealth characteristics to be collected.The attempt to undo those consequences resurfaced earlier this month when President Recep Tayyip Erdoğan used the NATO Summit in Ankara and a meeting with Trump on its side-lines to press for readmission to the F-35 Joint Strike Fighter programme.It is against this backdrop that, according to recent Wall Street Journal and other Western media reports, Ankara is now exploring ways of divesting itself of the S-400 – including, reportedly, a possible transfer to the United Arab Emirates – as part of a wider bargain with Washington on the F-35s. These reports remain unconfirmed, and any such transfer would require Moscow’s consent and would correspondingly necessitate overcoming formidable political, legal, and regulatory hurdles within the US government, especially in Congress.Whether Turkey ultimately succeeds in persuading Washington to overlook its acquisition of the Russian S-400 system and restore defence ties, including a return to the F-35 programme, remains uncertain. But the negotiations themselves are revealing.They serve to underscore a broader reality: operating and retaining the S-400 continues to cast a long shadow over defence relations with the US, particularly under Trump’s administration, and demonstrates that major Russian-origin weapon systems can carry enduring strategic and political costs in Washington.Against that backdrop, Delhi’s current trajectory appears all the more striking as on March 27, the Defence Acquisition Council (DAC), chaired by Defence Minister Rajnath Singh, accorded Acceptance of Necessity (AoN) approval for the procurement of five additional S-400 regiments as part of a Rs 2.38 lakh crore package.The Indian Air Force has already inducted three of five S-400 regiments acquired in 2018 for $5.43 billion, of which the fourth system is presently on its way by sea to India following extended delivery delays caused by the Ukraine war, while the fifth is expected by the year-end. And, should the proposed follow-on S-400 purchase be concluded, India will effectively double its S-400 inventory from five to ten regiments.Simultaneously, industry and security sources said the IAF is examining the possible acquisition of at least two squadrons of Russian Sukhoi Su-57 fighters – or around 40 platforms – as an interim solution until India’s indigenous Advanced Medium Combat Aircraft (AMCA), intended to deliver a similar fifth-generation capability, enters service in the mid-2030s.While neither the IAF nor the government has formally confirmed that such a proposal is under consideration, official sources said it was being driven largely by Pakistan’s expected induction of China’s J-35A stealth fighter over the next two to three years, creating what the IAF fears could be a significant capability gap unless ‘bridged’ by a comparable platform. Viewed alongside the planned acquisition of five additional S-400 regiments, however, the possible Su-57 procurement points not towards a significant expansion in India’s dependence on Russian military hardware.Furthermore, these developments are unfolding at a juncture when Washington’s tolerance for countries maintaining major economic ties with Moscow is visibly wearing thin. India and China – the world’s two largest buyers of Russian crude – have come under pressure, with Trump publicly threatening secondary tariffs of up to 100% if Moscow fails to meet US demands over ending the Ukraine war.Also read: India Could Trigger US’s CAATSA Penalties by Buying More Russian S-400sA bipartisan sanctions bill before Congress would further strengthen that approach by giving the US President clearer authority to impose similar penalties. Neither measure has yet become law, but together they indicate a growing willingness in Washington to use economic pressure against countries that continue maintaining significant economic ties with Moscow.That broader hardening of policy is also extending beyond defence equipment and energy.Additional duties on Indian pharmaceutical exports have also entered Washington’s policy debate, adding another potential pressure point in an already strained economic relationship. Given India’s central role as a supplier of generic medicines to the US market, any escalation in this area would further complicate bilateral ties. Consequently, defence industry officials in Delhi and Bengaluru are questioning whether Russian military procurement can realistically remain insulated from a wider deterioration in bilateral economic relations between Delhi and Washington.“From Washington’s perspective, India’s expanding economic and military engagement with Moscow is becoming increasingly difficult to treat as separate issues,” said a senior defence industry executive, who requested anonymity because of the sensitive nature of this issue. Continued purchases of discounted Russian crude, additional S-400 regiments, a possible Su-57 acquisition and expanding defence-industrial cooperation with Moscow, he cautioned, risk eroding the political willingness in Washington to continue shielding India from action under CAATSA.Until now, Delhi has consistently argued that its dependence on Russian military equipment was the consequence of decades of Soviet-era defence ties and inherited platforms—the accumulated ‘burdens of history’—rather than a reflection of a present-day strategic preference for Moscow. That explanation carried considerable weight in Washington, given that nearly two-thirds of India’s in-service military equipment originated in the former Soviet Union or Russia, making rapid diversification neither financially nor operationally feasible. Washington largely accepted this reality as penalising India under CAATSA would have weakened, rather than strengthened, its own Indo-Pacific strategy of balancing an increasingly assertive and militarist China.But CAATSA waivers are political judgments, not permanent guarantees.A cross-section of security analysts and defence industry executives warned that every fresh major military purchase from Russia made it ‘politically harder’ for Washington to continue looking the other way. Moreover, the cumulative effect of an expanded S-400 inventory, a possible Su-57 acquisition and sustained purchases of discounted Russian crude would reinforce the view within sections of the US administration and Congress that India’s dependence on Moscow no longer reflected inherited military realities, but had evolved into an active strategic choice. Consequently, the political argument for continuing to shield India from action under CAATSA could become difficult to sustain.None of this, however, means sanctions are inevitable.Also read: Despite US, India-Russia Defence Cooperation Remains a Necessary Pillar of New Delhi’s Security StrategyWashington still has compelling strategic reasons to exercise restraint, and few serious policymakers in the US wish to push Delhi back towards Moscow. But one of the principal strategic rationales that has underpinned that restraint is itself beginning to weaken.The Indo-Pacific construct – which for more than a decade elevated India to a pivotal position in American strategic thinking – has lost some of its earlier prominence as Washington’s focus increasingly shifts towards the Western Pacific and the intensifying military competition with China.The erosion of that framework has also been reflected in the changing fortunes of the Quadrilateral Security Dialogue (Quad) – the grouping of India, the United States, Japan and Australia, first established in 2007, allowed to lapse in 2008, and revived in 2017 in response to China’s growing military assertiveness.Once promoted as the diplomatic centrepiece of Washington’s Indo-Pacific strategy, the Quad has lost some of its earlier momentum, with fewer high-profile initiatives and a noticeably lower political profile in recent months. That evolving geopolitical landscape could make it progressively more difficult for the Trump administration to justify repeated political exemptions under CAATSA if India’s military and economic engagement with Russia continues to expand.India’s long-practised policy of strategic autonomy and multi-alignment has allowed it to balance Washington and Moscow, while extracting advantages from both relationships, but that balancing act may now be approaching its limits. The question is no longer whether Washington is prepared to keep overlooking India’s expanding defence relationship with Russia, but whether Delhi is willing to jeopardise access to advanced American weaponry, technology and industrial partnerships to deepen its materiel dependence on Moscow.This piece was first published on The India Cable – a premium newsletter from The Wire – and has been updated and republished here. To subscribe to The India Cable, click here.