Jamie Dimon, a frequent critic of President Trump’s first term, has been more conciliatory this time around, regularly complimenting the administration’s corporate tax cut extensions and slashing of bank regulations, and finding reasons to compliment aspects of Mr. Trump’s approach to immigration.

On Tuesday, however, the chief executive of JPMorgan Chase went out of his way to take exception to Mr. Trump’s posture toward Jerome Powell, the chair of the Federal Reserve. Mr. Trump and his allies have been withering toward Mr. Powell, whom they blame for not cutting interest rates and have accused, with no evidence, of political bias.

“Playing around with the Fed can often have adverse consequences — the absolute opposite of what you might be hoping for,” Mr. Dimon told reporters after his bank’s quarterly earnings release.

Mr. Dimon said that he hoped Mr. Trump would not attempt to replace Mr. Powell before the end of the chair’s term next spring, and that the president would support a replacement who was independent.

There is deep support on Wall Street for preserving a Fed that is apolitical and free from White House meddling, which they view as a linchpin of America’s free market system. And in other ways, Mr. Dimon has an interest in standing up for Mr. Powell, because the Fed regulates JPMorgan and other big banks.

Still, it was a rare moment for a high-profile banker like Mr. Dimon to come so directly to Mr. Powell’s defense. Mr. Dimon is perhaps the most closely followed executive in finance (and privately supported former Vice President Kamala Harris in last year’s election).

Mr. Dimon’s vocal support for Mr. Powell in the face of Mr. Trump’s attacks might seem relatively muted, but most big names on Wall Street have gone to great lengths not to talk about Mr. Trump’s polarizing policies at all.