The movement to break up the biggest banks has gained considerably more traction than many of the industry's most vocal defenders expected, the former Chairman and Chief Executive of JPMorgan Chase (JPM) said.

William B. Harrison, Jr. has been one of the big banks' most outspoken defenders in the past year, arguing for the utility of the biggest banks in speeches and opinion columns. His arguments have not silenced the regulators, lawmakers, pundits or even some fellow bankers, however, who continue to advocate dismantling of large, complex financial institutions, including JPMorgan Chase.

"I have been surprised by the traction on this subject," Harrison said in a video interview with American Banker recently. "It's gotten more traction than I would have hoped, or liked, or thought."

The renewed debate over a big bank breakup was effectively sparked last summer by one of Harrison's fellow industry veterans, former Citigroup (NYSE:C) Chairman and CEO Sandy Weill. Since then, top regulators have expressed support for the idea; Richard Fisher, president of the Federal Reserve Bank of Dallas, has called for the biggest banks to be dismantled. And in Congress, a bill that would effectively do just that has been offered by Sens. Sherrod Brown, D-Ohio, and David Vitter, R-La.

Some bankers are pessimistic about the industry's ability to continue rebuffing breakup attempts, especially in the wake of ongoing controversies involving JPMorgan Chase's London Whale trading losses and several large banks' efforts to manipulate the Libor rates. Zions Bancorp. (ZION) CEO Harris Simmons recently warned that big banks are "one major misstep" away from being broken up.

Harrison is less concerned about an imminent breakup.

"It would certainly be negative, but I just don't know what would be a tipping point, because right now I don't think it will happen," he said.

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