I agree it would be disastrous, Brennan does give reasons for why it would be; his reasoning is convoluted and can be ciphered by reading between the lines. First his argument is that it is not good for a new president to tear up agreements by a former president as it is "almost unprecedented", so reading between the lines such an act would ruin obama's already extremely weak and perverted legacy, so yeah that would be disastrous not only for zero but Brennan himself.
Second reason is even more convoluted "it could lead to a weapons programme inside of Iran that could lead other states in the region to embark on their own programmes, with military conflict". I guess he would have us believe this is not already happening as a result of this stupid agreement that encourages other states to do likewise as the U.S. gerously finances the very same endeavors.
Typical Progressive Liberal Democrat Socialist Drivel and they are all to eager to drink from the disgusting communist spittle cup.