US President Donald Trump has indicated some harsh measures against India for the S-400 deal with Russia. New Delhi concluded the deal with Russia on October 5, asserting that the deal is in its national interest and that the negotiations preceded CAATSA by a long period

New Delhi — Any kind of sanctions on India over the S-400 air defence missile system will place a big question mark before Indo-US relations and in fact will prove counter-productive for the US, says a senior defence analyst, who also served in the acquisitions wing of India's Defence Ministry. 
"It places [a] big question mark before the India-US relation which, had been on the upswing for quite some time. In fact, the sanctions will prove counterproductive and it will further bring India much closer to Russia than ever," Amit Cowshish, a former financial adviser (acquisition) to India's Ministry of Defence, told Sputnik.
India and Russia signed a contract for Russia's S-400 air defence system on October 5 during President Vladimir Putin's visit to New Delhi. India termed the purchase a necessity for national interest, while hoping for a waiver under the punitive Countering America's Adversaries through Sanctions Act (CAATSA).

"India will have to live with the sanction. It will have to find alternative ways of meeting the defence requirement, which it thought the USA could meet. On the issue of fighter aircraft, Russia, France, and Sweden will help India anyway as [they] did in the past," Amit Cowshish added.

Except for some aircraft, the US has not sold India any of its major defence equipment or technology, despite several rounds of talks under the Defence Technology and Trade Initiative. The Indian government has been looking at countries such as Israel and France, other than Russia, as far as the requirements of armed drones or other defence technologies are concerned.