Prime Minister Narendra Modi has ushered in a golden age for the BJP as the party made a comeback to power in Bihar after Chief Minister Nitish Kumar relegated coalition partner Rashtriya Janata Dal (RJD) to the Opposition last week, notes a top Indian-American think-tank.

"The upheaval is only the latest signal that the BJP is the new centre of political gravity in a country long controlled by the storied Nehru-Gandhi dynasty of Congress Party," Milan Vaishnav, director and senior fellow of South Asia Program at the Carnegie Endowment for International Peace said in an op-ed yesterday.

The BJP not only occupies prime position for the country's next general election -- scheduled for 2019 - but it is also moving at "breakneck speed" to cement its hold over powerful state governments, he wrote.

"Although the BJP government's gathering strength, signals policy stability and political consolidation, it simultaneously raises concerns about the health of India's democratic checks and balances," Vaishnav said.

Touting his business-friendly policies, nationalist rhetoric, and an aspirational appeal that struck a chord with a young and increasingly restless India, Modi led his party to a historic electoral rout, he said.

"Securing the first single-party parliamentary majority in three decades, Modi has ushered in a golden age for the BJP," he wrote in his op-ed.

Noting that the BJP's momentum has opened up "unprecedented opportunities" for the party, Vaishnav wrote, in the longer term, the addition of Bihar will hasten the arrival of the BJP's majority in the upper house, whose members are indirectly elected by India's state legislatures; this could materialise as soon as late 2018.

"With control of both legislative chambers, the BJP can push through its legislative agenda with few impediments," the Carnegie scholar wrote.

At the same time, he warned that this concentration of power also has its downside.

"The BJP, which has rapidly centralised authority under Modi and party president Amit Shah, would do well to heed the lessons of the past," Vaishnav said.

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