New Delhi, Dec. 6 -- It is clear by now that we need a large dose of fiscal stimulus to rev up the engine of growth. All eyes are on India's Union Budget that will be presented in a couple of months. The size of the stimulus will be determined by constraints on borrowing capacity, debt servicing and concerns about India's sovereign rating. A downgrade would increase the cost of borrowing not just for the government, but for the private sector as well; it could also trigger an automatic freeze on portfolio funds that passively follow indices and have been pouring into India. Such a freeze could in turn strain the rupee's exchange rate, which might fall abruptly. The risk of a sudden stop or reversal of international flows is very real, and c...