Dr Sen has been one of the most approachable of Ambassodor. That has also made him vulnerable. Aziz made full use of this access and chose to abuse the access he was given. Dr Sen's work in promoting Bharat's interests has never been in doubt.
I well understand his frusteration. I do not doubt that Bharat did its best in the negotiations, but in healthy polity decisions are made in an environment of robust and honest debate.
It is quite clear that the 123 Agreement was written by America with that its one sided tilt to America is inescapble. It is not a document to which Bharat could put its signature in its present form. Of course America would like to bind Bharat to it, but leaders of country of a billion people are not going to persuaded by the inconvenience America and indeed the world is put by our refusal to be ensnared or enslaved in such a way.
