WASHINGTON: The US is likely to eventually grant a waiver to India for its mega $5.43 billion acquisition of five Russian S-400 Triumf air defence missile squadrons after some turbulence in bilateral ties, as per the assessment of several government officials, defence analysts and foreign policy wonks here.

President Donald Trump, who set matters aflutter with his ominous "India will soon find out" cryptic remark on the S-400 deal inked earlier this month, will of course be the final arbiter. "Trump is known for his unpredictable ways, and often ignores advise even from his own experts," said an analyst.

Both US defence secretary Jim Mattis and secretary of state Mike Pompeo, who were in India for the two-plus-two dialogue on September 6, have strongly backed India's case for a "national security waiver" under CAATSA (Countering America's Adversaries through Sanctions Act), which seeks to prevent countries from buying Russian weapons or Iranian oil.

But the jury is still out. The presidential waiver for the S-400 deal, if and when it's granted, will come with caveats, say experts. One, the Trump administration will need a transactional quid pro quo in terms of a major Indian defence deal for the US.

Two, India will have to visibly demonstrate a strategic decision to progressively reduce its dependence on Russian weapon systems. Three, if India goes in for another big arms deal with Russia, like the impending lease of a second Akula-class nuclear-powered submarine for over $2 billion, it will further muddy the waters. "Repeated waivers will be tough," said an expert.

Senior state department official Alice G Wells, on her part, said, "The US government is committed to enforcing the legislation (CAATSA). There is no country-specific waiver, no blanket waiver for any country. So, each transaction will be viewed on its own merits."

John Hopkins University professor Joshua T White, who also served in the Obama administration as a senior adviser on South Asia, in turn said, "The US sees Russia as a malign actor on the world stage, and has a valid interest in constraining its defence economy. It's a legitimate problem for Washington when India makes a multi-billion dollar purchase of the S-400 systems."

But White, like many others, believes sanctioning strategic partners like India is certainly not a good idea. "The CAATSA legislation was poorly written, and poorly revised, and its requirement of a presidential waiver sets a high political bar, particularly for this (Trump) administration. I think a waiver is likely but not before its generates political uncertainty in the relationship," he said.

India, of course, has told the US that the acquisition of the S-400 systems, which can detect, track and destroy hostile strategic bombers, fighter jets, missiles and drones at a range of 380-km, was an "urgent national security requirement" for it. 

The Modi government also dispatched top-level military technical teams to the US to assure the Trump administration that the operational secrecy of American weapon systems will never be compromised or leaked to third countries by India, as was reported earlier by TOI. 

But there is also consternation in the Indian government, which got reflected in defence minister Nirmala Sitharaman's dismissal of CAATSA as "a US law and not a UN law". The US, incidentally, has bagged lucrative Indian defence deals worth $17 billion over the last decade, even overtaking Russia for a couple of years. 

There are more in the pipeline. The US is pushing for the F/A-18 or F-16 fighter production line in India to supply 114 jets for the IAF for $20 billion. The F/A-18 is also a strong contender in the Indian Navy's quest to induct 57 fighters to operate from aircraft carriers. American helicopters are also in the fray for the proposed projects to acquire 111 naval utility and 24 multi-role choppers. "Sanctioning India will be counter-productive for the US," said another expert.