The biggest threat to Hindutva is a unity muslim political class. Think about it, Brahmins control the hindutva narrative and they are maybe 5-8% of all hindus in India (50-80m). Yet they are able to manipulate backward classes and dalits for their own advantage.
Hindus are inherently divided along religion/caste lines, whereby sunni islam is the largest single religious block in the subcontinent numbering around 500+ M. That in itself as a political group is powerful that would be able to take advantage of caste divides amongst hindus... This is the exact strategy the mughal empire employed.
Brahmin know this that is why the RSS is willing to make amends with buddhist, sikhs, jains, christians and even Shias but never with Sunnis. They fear Sunni unity because once our people are united then Shias fall in line pretty easily followed by dalits and then sikhs which united are 1+B. In all of 5000 years in the Indian subcontinents only the Muslims were able to outsmart the brahmins.
