“This board, historically, has been viewed as a board that was there on paper,” said Charles M. Elson, a corporate governance expert at the University of Delaware, who owns shares in Bank of America and voted against the Merrill merger. “But the question has been how active they have been in overseeing the C.E.O.?”

Bank of America’s board is an eclectic group, and it will grow larger this week when it adds three members from the board of Merrill. The bank’s two most powerful directors, O. Temple Sloan Jr. and Meredith R. Spangler, are close to Mr. Lewis’s predecessor, Hugh L. McColl Jr., who began building the company into the banking giant that it is today. Mr. McColl, still an influential pillar at the bank, has said in recent days that he supports Mr. Lewis. But if he changed his mind, Mr. Sloan and Mrs. Spangler would likely follow his lead, according to people with knowledge of the board’s thinking.

Four of the current members were around a decade ago when the bank took its current name after acquiring a California rival. Another handful joined in 2004, when Bank of America acquired FleetBoston. Another was an executive at MBNA, the credit card company the bank acquired, aiming to build the bank into a credit card powerhouse.

Aside from Mr. Lewis, only two people on the board  the former chief of FleetBoston and a former senior executive of MBNA  have roots in banking. While Wall Street is rife with tales of bank and brokerage directors who deferred to executives seeking faster growth through ever-riskier business, Bank of America’s shareholder advocates have grown increasingly concerned about the board’s ability to understand financial risks and rein in managers.

Until recently, Mr. Lewis was hailed as one of the saviors of Wall Street. He bought the troubled mortgage lender Countrywide and agreed to buy Merrill at the height of the financial crisis with no federal support. But by the time the merger closed, Merrill’s losses were larger than expected. The government soon handed Bank of America another multibillion-dollar cash infusion.