“I for one,” Mr. Issa told the Fed chairman, “am looking at Main Street America, the stockholders who in some cases got less than they would have gotten through other means. This includes Chrysler, General Motors and, of course, Bank of America and Merrill Lynch.”

Mr. Issa did not mention his own extensive links to Merrill Lynch.

In a television interview days later, however, he said: “I bank at Merrill Lynch. I’m very well aware that every broker there, all the people who were stockholders, were furious that they were in fact being fire-saled to them.”

And Mr. Issa is no ordinary Merrill customer.

His transactions there have totaled more than a billion dollars in the last decade, records show. In the aftermath of the firm’s acquisition in September 2008, in fact, he bought and sold at least $206 million in Merrill Lynch mutual funds in the next 15 days, records show.

His ties to the bank deepened last year, records show, as Merrill Lynch gave him two “personal notes” for lines of credit worth at least $75 million.

Likewise, Mr. Issa has aggressively defended Goldman Sachs, another Wall Street giant.

When the Securities and Exchange Commission brought a major lawsuit charging Goldman with fraud last year, Mr. Issa fired back by opening an investigation. The timing of the lawsuit, he said, smacked of a “partisan political agenda” meant to help President Obama and bolster a bill overhauling financial regulations.

His charge drew nationwide attention, putting regulators on the defensive, but the S.E.C. inspector general later found “no evidence” of political meddling.

Mr. Issa came to Goldman’s defense again last month in a letter to regulators complaining about restrictions on financial firms. Broker dealers “such as Goldman Sachs” faced “a substantial reduction in leverage” because of excessive capital requirements, he wrote.

As with Merrill Lynch, Mr. Issa is keenly interested in Goldman’s performance.

A few weeks before opening his inquiry into the Goldman lawsuit, in fact, he bought another large batch of shares in one of the firm’s high-yield mutual funds, records show. By the end of the year, his stake in Goldman’s fund was worth as much as $25 million.