Many analysts believed the Mumbai attacks would be devastating for the Indian Congress Party--the pro-business and pro-US ruling party in New Dehli. While Pakistani cells were almost certainly responsible, a number of intelligence failings on the part of Indian counterterrorists became apparent. The US had warned India of a terror attack on Mumbai through its ports.
Such failings looked like they would vindicate BJP (the opposition leader) criticisms for years over weak terror and Pakistan policies. But Congress is holding on with surprising vigor. In recent state elections, Congress won 3 of 5--most interestingly, Dehli, which pundits thought seemed certain to go to BJP due to its close cultural ties with Mumbai. But while the bombings were clearly a black mark on Congress, the relative responses of Congress and BJP may have made the difference.
Congress has stepped up pressure on Pakistan, together with the United States. India has demanded--and to some extent, received--Pakistani help during the Mumbai investigations. Quickly, the Pakistanis responded with a number of arrests, including the alleged "mastermind" of the attacks. In addition, the government has revealed the identities of the Mumbai gunmen, giving the Pakistanis few political options besides a new wave of arrests to get to people near these published gunmen that might have been involved in conspiracy. Indians may be relatively satisfied with this cautious but firm response. It appears dynamic and well-thought-out.
BJP, on the other hand, has faced accusations of "opportunism." The Mumbai attacks were much like an Indian 9/11, and appearing to try to gain politically by the event will hurt any party. BJP may have been too aggressive. In addition, Indians may not want to encourage another bloody war with Pakistan (that might, if poorly designed, lead to even more terrorism by fracturing the Pakistani state) by electing the currently fevrishly militant BJP.
Elections in May are coming up for Congress, and they can't afford to lose. Allegations of buying votes on the US nuclear deal remain, and the Congress response to these attacks may shape their election hopes in May. They have a few months to make it work, which may be the basis of their slow, cautious approach. If Pakistan does end up declaring full-scale war on the militants, then Congress can take credit for applying enough pressure to get the job done without having so sacrifice Indian troops--such an outcome would be the best Congress can hope for.