MUMBAI, India — He does not act the part. At 76, Subramanian Swamy has a youthful demeanor, is frequently cheeky but is almost always composed. Yet he is arguably the most vicious infighter in Indian politics, where he has spent a career of more than 40 years taking down ministers and governments. Lately, he has been on a roll.

First, he drove out India’s central bank chief.

Next he set his sights on the chief economic adviser to the Finance Ministry.

Then he made a veiled attack on the finance minister for wearing a business suit on a trip to China instead of traditional Indian garb, saying he looked like a waiter.

In the process, Mr. Swamy, an economist, has become the subject of intense controversy, an unapologetic Hindu nationalist whose antics are increasingly threatening the stability of the government of Prime Minister Narendra Modi. Now, the question is whether Mr. Modi will be able to keep him on a tight enough leash to prevent him from cannibalizing his government.