Lawrence H. Summers, who served as Treasury secretary under President Bill Clinton, has become a frequent and pointed critic of Steven Mnuchin, the current Treasury secretary.

WASHINGTON — It is an unwritten rule that if a former Treasury secretary has nothing nice to say about one of his successors he does not say anything at all. But in the nation’s capital these days, the rules of political comity are meant to be broken.

Raising eyebrows in economic circles, Lawrence H. Summers, the mercurial Treasury secretary for President Bill Clinton, has leveled a barrage of increasingly personal criticism at the current Treasury secretary, Steven Mnuchin.

In podcasts, blog posts, op-eds and on Twitter, Mr. Summers, the former president of Harvard and a top economic adviser to President Barack Obama, has accused Mr. Mnuchin of damaging the credibility of Treasury by making “irresponsible” economic assessments of the administration’s tax plan and acting as a “sycophant” to President Trump.

The attacks have alternately amused and angered those who run in economic circles, with some saying it is Mr. Summers who is damaging the credibility of the office by leveling public attacks on a sitting Treasury secretary.

“For me we have a tradition for people who have been in the position not to criticize current secretaries,” said Paul H. O’Neill, who served as President George W. Bush’s first Treasury secretary. “That doesn’t mean we don’t have an opinion, but we don’t tell people what we think.”

But, he added: “Larry is his own guy.”

While Treasury secretaries have all had varying degrees of success and influence, those who have held the job generally agree that heckles from predecessors are not helpful.

“From what I can remember, no one really talked badly about others,” Franklin Noll, president of the Treasury Historical Association, said of former Treasury secretaries. “It doesn’t pop into my head because it didn’t happen.”

Some have been taken aback by the personal nature of Mr. Summers’ criticism of Mr. Mnuchin.

“I think criticism is best when it’s specific — if there’s a particular statement or policy that you disagree with, say why,” said Glenn Hubbard, the dean of Columbia Business School and a former deputy assistant Treasury secretary. “You don’t really need to be ad hominem.”

Larry Kudlow, an economist who calls himself a friend of Mr. Mnuchin…