musings on migrants and bengali identity

I think its accurate to say that in Calcutta, you see the chauvinism of the Bengali intelligentsia, but it doesn't have overt political manifestations like it does in Mumbai. One of the questions that I hope to get a handle on while I'm here is why this is the case. Why don't political parties in West Bengal exploit the migrant/native cleavage?
I think the first part of the answer is that they do, but more subtly than in Bombay. In Calcutta, it seems politically incorrect to speak out against migrants. Maybe it has to do with the way the city's political language was formed, with its historical roots in the Bengali enlightenment as well as the last 3 decades of Communist Party rule.
On that front, I've been thinking that maybe the relative religious tolerance in West Bengal is one route to understanding its migrant politcs as well? Communal politics (Hindu-Muslim competition) isn't a stark aspect of politics in West Bengal like it is in other parts of India. The BJP, for example, has almost no presence here. This is typically explained by the two trends I mentioned above:
1. The Bengali literary and philosophical enlightenment period of the late 1800's has enabled Bengalis to form a Bengali identity over a primarily Hindu or Muslim one, and so to rise above the communal divide
2. The Left Front government, stable in power for 3 decades, has managed to maintain power because it stands for all workers and does not exploit Hindu-Muslim tensions
And yet, there are religious divisions that are quite apparent in Calcutta, even if they don't manifest themselves in political rhetoric. For example, it seems to be a more segregated city than Mumbai. There are some areas, like Raja Bazaar, where there are concentrations of Muslims. And a few pockets of the city that are like Muslim ghettos (and you see very few Muslim women, in hijab, elsewhere in the city). Another indication is that Muslim Bihari migrants tend to be significantly poorer than Hindu ones. So the two reasons for the lack of religious tensions that I listed in some ways hide the communal divides in Calcutta.
Similarly, there is definitely an undercurrent of anti-migrant thinking here, even if it is politically incorrect for a mainstream politician to say that migrants should not be welcome. I found an organization called Amra Bangali, which is kind of a fringe Bengali chauvanist political pressure group. Among their demands is a Bengali regiment in the Indian army, job reservations for Bengalis in both public and private service in West Bengal, and no land transfers to people outside of Bengal. They claim that as you move from downtown Calcutta to the outer areas of the city, the population of Bengalis gets higher, which indicates that natives are being pushed out of downtown and into the suburbs (by migrants). So while their platform sounds similar (yet more extreme) than Mumbai's anti-migrant party (the Maharashtra Navnirman Sena), they actually don't have anywhere near the infamy or political following that the MNS does. Its more... sub-culture. Still, Dr. Das at the University of Calcutta said he has a strong feeling that there is an underlying anxiety, even among mainstream parties and the general population, that newcomers from Bihar have cut into local jobs and culture. And maybe these things are also masked by the strong strain of enlightened, leftist thought in Bengali culture.
So another thing I have to find out is whether the outcomes for migrants into this city--like their ability to get idenitity documents, how they are treated in bureacratic settings like rationing offices, their ability to vote-- whether these experiences are similar to those of rural migrants from West Bengal, or native Calcuttans, or whether there is a marked difference that seems to stem from other prejudices.