Richard Rossow, a Washington D.C-based observer of India, told Business Insider that even under the new President, US will oppose New Delhi’s $5.5 billion deal with Russia for the S-400 missile. The Donald Trump administration had even hinted at punitive action against India for its defence deal with Moscow

“This might be the single biggest obstacle in India-US relations in the next few years,” Rossow, a senior adviser and the Wadhwani Chair in US-India Policy Studies at CSIS, said in an interview.

Donald Trump is gone and Joe Biden is in as the 46th President of the United States. India may cheer the fact that US has joined the Paris Climate Accord, and that immigration to US via H-1B visas may become easier for Indian talent, and many other positive changes that may occur.

However, one thorn in the flesh in India-US relations is already visible: New Delhi’s $5.5 billion deal with Russia to buy the S-400 missile. A Washington D.C-based, keen observer of India, believes that this could be the “single biggest obstacle” even under the Biden regime.

The S-400’s anti-missile system’s radar has a range of at least 600 kilometres for surveillance. And, it can track a large number of targets simultaneously. According to experts, this will help India form an interlocking grid of missiles to cover all its bases.

US has been vehement in its opposition to India’s defence deals with Russia. “There is within the US sanctions authority, Countering America's Adversaries Through Sanctions Act (CAATSA), there is a narrow waiver included in the CAATSA legislation. But the waiver authority is still very narrow and there are still questions about which countries will be able to make it through,” Richard Rossow, a senior adviser and the Wadhwani Chair in US-India Policy Studies at CSIS, told Business Insider in a recent interview.

India has bought five Russian Almaz-Antei S-400 Triumf self-propelled surface-to-air (SAM) systems and the deal was signed during Russian President Vladimir Putin’s visit to India in October 2018. The delivery of the first batch of the Triumf-made air defence system was scheduled to reach India by the end of 2021.

However, the deal had got massive opposition from the Trump administration, which had even hinted at punitive action against India. Trump said India should drop the deal to avoid a diplomatic crisis.

A similar deal that Turkey struck with the Vladimir Putin-led government in Russia led to sanctions against Ankara. “We urge all of our allies and partners to forgo transactions with Russia that risk triggering sanctions under the CAATSA. CAATSA does not have any blanket or country-specific waiver provision,” a US embassy spokesperson told Reuters.

For Modi, it’s a difficult dilemma. On one hand, it needs America as a strong ally who will stand with it and take on China, which has been aggressive at India’s borders. On the other hand, it will have to manage its relationship with Russia rather delicately, given the latter is more friendly with China than most other countries in the world.

There is also the issue of optics. India would rather not be seen as being arm twisted by the Pentagon into buying American weapons.