The concern is that those statements — made months after Mr. Dimon learned the trades had breached the firm's internal alarm system hundreds of times, according to the Senate report — could put the bank in a precarious situation with regulators investigating the trades.
And government officials who would speak only anonymously say that Mr. Dimon, faulted in the Senate report for strong-arming regulators, is also losing sway with some authorities in Washington.
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Mr. Dimon has already apologized for the $6 billion trading loss, and his compensation has been halved.
And he does maintain cordial ties to several important lawmakers, including Senator Elizabeth Warren, the Massachusetts Democrat and a fierce critics of the bank. Last week, he met with Treasury Secretary Jacob J. Lew.
Still, the recent attention to the trading debacle could diminish Mr. Dimon's influence in Washington at a time when the final drafts of important bank regulations are still being written. It also could provide momentum to a vocal minority of investors seeking to loosen Mr. Dimon's grip on the bank.
"It's clear from the Senate report and Friday's hearing that senior executives not only misinformed investors and regulators about the excessive risks the bank was taking, but also withheld this information from their own board," said John C. Liu, the New York City comptroller who has invested in $500 million worth of JPMorgan shares on behalf of public pension funds. "Mr. Dimon's failure on this score comes from the hubris of having too much power placed in his hands."
Mr. Liu hopes to bolster support for a shareholder proposal that would split JPMorgan's chief executive and chairman roles. The nonbinding measure received 40 percent backing last year and is expected to gain new votes.
But it could still fall short. And Mr. Dimon, a native of Queens, is showing few signs of changing.
He continues to scold regulators for their crackdown on Wall Street risk-taking. Last summer, he told an audience that the so-called London Whale — the JPMorgan trader who placed the outsize derivatives trades at the center of the bank's losses — has been "harpooned."
And at the bank's investor day last month, Mr. Dimon jokingly dismissed a question from an analyst, Mike Mayo, by saying "I'm richer than you."
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"When Jamie gets challenged, you get an image that he's back at a Queens playground, ready for a fight," Mr. Mayo of Crdit Agricole said.
The report, issued by the Senate's Permanent Subcommittee on Investigations, also angered Mr. Dimon, according to a person close to the executive. By his reckoning, the report exaggerated claims that the bank had misled regulators about the trading loss.
"Our management always said what they believed to be true at the time," said Joe Evangelisti, a bank spokesman. "In hindsight, we discovered some of the information they had was wrong." He added that "The New York Times is blowing out of proportion a lighthearted exchange between" Mr. Dimon and Mr. Mayo.
Mr. Dimon's supporters, including several shareholders, also argue that he has good cause to be arrogant. Even with the trading loss, Mr. Dimon in 2012 produced the bank's most profitable year ever.
He also was quick to strike a note of contrition when the trading losses spun out of control last year. And while he was not asked to testify on Friday, he did appear at two Congressional hearings last summer.
"Jamie apologized and took responsibility on live television, multiple analyst calls, and in testimony before Congress and the Senate," Mr. Evangelisti said.
But Mr. Dimon's critics point to the Senate report, which revealed that he was informed for months about potential problems with the trading position at the bank's chief investment office. Rather than rein in the risk, the subcommittee found that Mr. Dimon had allowed the bank to alter its internal alarm system in January 2012, enabling the traders to continue building the big bets. While Mr. Dimon has said he did not recall authorizing the shift, the subcommittee cited an e-mail in which he said: "I approve."
Two months later, when chief investment office executives met with a "risk policy" committee of the bank's board, they failed to sound the alarms about the souring bet. The revelation suggests that Mr. Dimon possessed a wider window into the problems than his fellow board members.
After slashing Mr. Dimon's compensation in half, to $11.5 million, JPMorgan board members have largely remained unified in support of Mr. Dimon. Under Mr. Dimon, the bank has earned record profits and its stock has risen 27 percent over the last four months.
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After the trading loss, board members note, Mr. Dimon took swift action to fortify the bank's risk controls and unwind the trades. Mr. Dimon has reshuffled JPMorgan's executive ranks, fired traders involved in the losses and clawed back millions of dollars in compensation.
"So long as JPMorgan continues to perform, I assume he will have the board's support," said Sheila C. Bair, a former head of the Federal Deposit Insurance Corporation, who noted that the bank's performance "has been far superior" to rivals. "Given the size and complexity of JPMorgan's operations, what would their alternatives be?"
But a small fraction of the 11-member board is unhappy with Mr. Dimon, according to the people briefed on the board's thinking. Those members fault the chief executive for relying on assurances from his deputies that trades were manageable. There is also concern about the bank's relationship with its regulators.
Since the trading debacle, regulators have adopted a more vigilant stance with JPMorgan, according to two government officials embedded at the bank, saying that trust has waned.
The Senate report also paints a critical picture of Mr. Dimon's defiant stance with the bank's primary regulator, the Office of the Comptroller of the Currency. For a brief period in August 2011, Mr. Dimon stopped providing profit-and-loss reports about the investment bank to regulators, because he was concerned about a security breach. During an August 2011 meeting with the Comptroller's examiner-in-charge at JPMorgan to discuss the halted reports, Mr. Dimon took an adversarial tone, according to testimony on Friday from the examiner, Scott Waterhouse. Mr. Dimon pushed the regulator to explain why he needed that "level of information," arguing that oversight could still be done "without it."
That attitude appeared to seep into the broader ranks of JPMorgan. Examiners who asked for more information were routinely met with resistance, the report shows.
When regulators with the comptroller's office pressed for details in early 2012 about variables the bank was using to calculate its stress test, the bank resisted.
"Even that was treated like a blasphemous request," said an examiner who insisted on anonymity for fear of retribution.