Most theorists consider that the key responsibility of an embedded power group is to challenge the assumptions that comprise the group's own mindset. According to these commentators, power groups that fail to review or revise their mindsets with sufficient regularity cannot hold power indefinitely, as a single mindset is unlikely to possess the flexibility and adaptability needed to address all future events. For example, the variations in mindset between Democratic Party and Republican Party Presidents in the U.S. may have made that country more able to challenge assumptions than the Kremlin with its more static bureaucracy.