Flanked by a coterie of lawyers and lobbyists, Kenneth D. Lewis, Bank of America’s embattled chief executive, walked into yet another Congressional hearing room on Thursday as the sole witness in a merger drama that has shadowed his banking empire for months.

But this time, lawmakers turned the spotlight on personalities who were not seated in the chamber: the federal officials who had pushed him to complete a troubled merger with Merrill Lynch late last year, despite knowing that huge losses riddled the once-mighty Wall Street firm.

Those officials, most prominently Ben S. Bernanke, the chairman of the Federal Reserve, and Henry M. Paulson Jr., the former secretary of the Treasury, will be called to testify before lawmakers soon. But the twists and turns of their conversations with Mr. Lewis came into full view on Thursday, through scores of e-mail messages and other documents from the Federal Reserve and Bank of America obtained by The New York Times.

Bank of America announced its deal with Merrill in September, as financial markets were seizing up and Lehman Brothers fell to its knees. But Mr. Lewis grew less certain once the bank discovered that Merrill’s finances were worse than imagined, and considered pulling out of the deal.