The CPI top brass on Tuesday reviewed the debacle of the Left in the recent assembly elections in its stronghold of West Bengal. A meeting of the party's National Executive in New Delhi, termed it as a serious political setback and decided to make joint efforts to regain their lost base. It also heard reports received from its units in West Bengal, Kerala, Tamil Nadu and Assam and held in-depth review of the Left's poll performance and reasons for the humiliating defeat in Bengal.The meeting came in the backdrop of party General Secretary A B Bardhan warning Left leaders to either change or perish.