First came Indian Prime Minister Manmohan Singh's narrow triumph in a no-confidence vote in parliament last month. Manmohan stood down fierce opposition from the left and, in a chaotic and unruly session, risked his governing coalition by forcing the vote.

Only weeks later, on August 1, the International Atomic Energy Agency signaled its approval of India's draft plan for inspection, clearing the second of four hurdles. Only the 45-member Nuclear Suppliers Group (NSG), where approval is likely, and the US Congress, where nothing is guaranteed, now stand in the way.

In Washington, supporters can trumpet the backing of political heavyweights - the George W Bush administration, Republican Senator John McCain, and, at least tentatively, Democratic Senator Barack Obama - but remain stifled by non-proliferation hawks and a frantic legislative calendar. (An arcane caveat to the nuclear deal requires that to call a vote, Congress be in consecutive session for 30 days after the NSG's approval. Short of an unexpected extension, this may not be possible.)

Yet the deal's advocates press on, mustering visions of a vast economic windfall and lucrative arms deal to follow, while behind closed doors emphasizing one selling point that appeals to both sides of the aisle: America must recruit the Indian tiger to hedge against the rising Chinese dragon.

Yet despite its broad popularity, this "unspoken" strategy is, well, "untested". Its proponents laud the "hedge" theory as a selling point for the nuclear deal and as a containment strategy for China, but few have asked the tough questions it provokes; namely, is this a realistic strategy, given the warming Sino-Indian relationship? And if India is unwilling to serve as America's deputy in Asia, does the nuclear deal deserve congressional support anyway?

Doubts about Washington's aspirations for New Delhi abound. Since the first days of independence in 1947, India's geopolitical orientation has been ingrained with a bias toward neutrality at the least; and on its worst days an outright anti-Americanism. The latter, a vestige of Cold War politics, is alive and well among India's politically powerful left, led by the Communist Party of India (Marxist). Their favored tactic - painting supporters of the deal as American puppets - remains a poisonous charge in Indian politics, and will remain so for years to come.

Further complicating Washington's vision is the historic thaw (recently elevated to a "strategic partnership") now underway in Sino-Indian ties. Diplomatic collegiality between the two Asian giants, including a series of limited but unprecedented joint military exercises, may be eclipsed only by the pair's booming trade relationship. Indeed, with two-way trade set to top US$40 billion, China this year will overtake the US as India's largest trading partner.

And yet, history and national identity are notorious for trumping raw economic interests in Asia. Consider the most fundamental of inter-state relations: a shared border. China and India's has been under dispute for nearly a century, and China has been testing New Delhi this year with a wave of abrupt but underreported incursions into Indian territory. Beijing still claims tens of thousands of square miles of Indian territory in the Indian states of Sikkim and Arunachal Pradesh, the subject of a 1962 border war.

China's incursions, in some ways routine by now, have become more numerous (anywhere between 60 and several hundred) and brazen (one crossing having driven a kilometer into Indian territory) in the past six months - an unusual provocation, given China's sensitivity to world opinion ahead of the August Summer Olympic Games in Beijing.

Were the border incursions an isolated incident, they would likely be swallowed by the mounting ties that bind China and India. But isolated they are not, and in 2006 a warning by China's ambassador to India put in question the warmth generated by a dozen of rehearsed summits: "[T]he whole of the state of Arunachal Pradesh is Chinese territory ... we are claiming all of that. That is our position." The point was not lost on the 1.1 million Indians living in a state the size of Maine. Indian diplomats from the state have even been denied visas by Beijing, which reminds them documentation is not required to travel their own country.

Ominous gestures like this add to the sense of anxiety generated by a host of Chinese policies in recent years. Years of Chinese military (and probably nuclear) assistance to India's arch-enemy, Pakistan, has earned it no friends in Delhi. Nor has China's assertive expansion into the Indian Ocean. Indeed, Beijing's plan to litter the South Asian coastline with a series of naval bases - its so-called "string of pearls" - has put India on the defensive in its own backyard. And abroad, a fierce competition for natural resources in Africa and beyond has swung decisively in China's favor, curtailing India's access to raw materials, and wounding New Delhi's pride.

Even the blossoming Sino-Indian trade relationship generates friction: where their account was only recently in balance, India has suddenly discovered a $10 billion trade deficit, ushering them into the same frustrated and indebted club as the US and European Union. Finally, China's expanding ballistic missile and space capabilities have kept Indian defense analysts on edge, as has China's clandestine submarine base on Hainan island.

But never mind China. Even if palpable Sino-Indian tensions don't breathe life into Washington's "hedge" strategy, the nuclear deal, and a deeper alliance with India, remain in America's interest. Why? Because India has been a crucial and enthusiastic ally in coalition efforts to stabilize Afghanistan; because India has proven that given a pluralistic environment, 150 million Muslims find no tension between Islam and democracy; because despite 8,000 kilometers of ocean and an acute culture gap, the two countries share a common belief in democracy and a common language; because - with GDP surging at 9% - India gives lie to the canard that economic growth is reserved for autocratic governments; and because, perhaps above all, India and America share the most fundamental of goals: cleansing the planet of fanatics who murder innocent people in the name of their fabricated religion. Remember, in recent years no non-Muslim country in the world has suffered more at the hands of Islamist extremists than India.

Legitimate non-proliferation and verification concerns, India's sporadically unconstructive stance towards Iran and Myanmar, and a series of potential loopholes written into the agreement justify a measured and critical approach to the nuclear deal. Congress is entitled, within reason, to seek assurances on such open-ended questions and to try to persuade (but not lecture) India where they disagree in geopolitics. At the same time, Congress must recognize the panoply of shared interests and common threats that bind the two countries, and fully grasp the potential of a true strategic alliance between the world's largest democracies.

Jeff M Smith is a research fellow at the American Foreign Policy Council in Washington, DC.