After former environment minister Jayanthi Natarajans letter to Sonia Gandhi shook up the Congress party last week, another letter is expected, that could be cataclysmic.

Dr Karan Singh, long-time Congress member and its Rajya Sabha MP, is learnt to have sent a four-page letter to Sonia expressing his disillusionment with the party.

The immediate reason? He was not included in the Congress delegation that met US President Barack Obama on January 26; his arch rival, Anand Sharma, whose overreach in matters international is said to rile Karan Singh no end, was.

Dr Singh has been feeling suffocated in the Congress for quite some time now, and would have quit the party last year had it not been for Sonia and Rahul meeting him over lunch and softening him up a bit, say insiders.

But now, matters are expected to come to a head in the wake of the Delhi election results in which the party is expected to fare badly.