The firing of White House Communications Director Anthony Scaramucci on Monday — just days after his hiring led to the departures of press secretary Sean Spicer and Chief of Staff Reince Priebus — has dispelled any wisp of hope that clarity might be coming soon to Donald Trump’s messaging operation. But improving that operation remains a presidential priority. After all, when asked months back to grade himself, Trump, unsurprisingly, gave himself an A, but added: “In terms of messaging, I would give myself a C or a C+. …  I think I’ve done great things — I and my people, but I don’t think we’ve explained it well enough to the American public.”

Trump’s instinct to deny serious shortcomings in his ideas or policies or leadership and admit them only in the seemingly grubbier realm of communication is one that’s all but universal among struggling presidents. Asked in 2010 to explain the Democrats’ losses at the polls, Barack Obama did the exact same thing, arguing that “we probably spent much more time trying to get the policy right” and fell short on “marketing and P.R. and public opinion.” Among recent presidents, George Bush the elder was also known for insisting that his plummeting standing stemmed from a communication failure, not any larger defects.

Alas, fixing a troubled communications shop or tweaking the president’s words or themes is rarely the ticket to renewed popularity. History suggests that an administration’s troubles in getting its message out usually result from underlying problems with policy. Many of Trump’s predecessors — including, notably, Presidents Herbert Hoover, Lyndon Johnson and Jimmy Carter — started out with a reputation as media wizards, only to have their communication skills questioned when their presidencies encountered trouble. Bad spin, it turns out, isn’t a cause of presidential difficulties but a symptom.

Herbert Hoover may be the best example. Elected handily in 1928, he was pronounced a modern master of the new arts of publicity. As commerce secretary in the 1920s, Hoover had led the rescue, relief and recovery effort after the 1927 Mississippi flood, shrewdly delivering on-site radio speeches so audiences could hear the river rushing behind him. His 1928 campaign team produced a blockbuster campaign film called “Master of Emergencies” that captivated theater audiences.

But with the October 1929 stock market crash, Hoover’s magic with his message dissipated. His inability to fix the worst economic downturn in U.S. history turned voters against him. He tried to compensate, correspondent Frederick Essary noted, with a “White House publicity machine” that churned out “daily presidential speeches, messages, proclamations, pronouncements, executive orders, appointments” and more — but to no avail. The White House even launched a newspaper that ran pro-Hoover puffery. It folded after three issues.

The president brought in the top spin artists of his day, including Albert Lasker of the Lord & Thomas advertising agency, Bruce Barton of BBDO and Edward Bernays, known as the father of public relations. But Bernays threw up his hands, insisting that “the purely inspirational and exhortative appeal” that the White House wanted would fail. What Hoover needed was an effective jobs program.

Lyndon Johnson’s fortunes as a communicator followed a similar trajectory. Early on, reviewers applauded his magnificent delivery of two historic speeches — his Nov. 27, 1963, address to Congress, days after John F. Kennedy’s assassination, promising to continue JFK’s legacy, and his May 1964 University of Michigan commencement speech laying out his “Great Society.” Pundits also praised his facility with television. In March 1964, Johnson sat for an hour-long on-air interview with reporters from the three networks, winning rave reviews for his eloquence and performance.

But as he escalated American military involvement in Vietnam and the public soured on the war, LBJ and his public relations team came under relentless criticism. The so-called credibility gap plagued him; though some of his untruths were simply the embellishments endemic to political life, he was cut no slack. Statements that would once have been indulged as routine fibs, exaggerations or human inconsistency were now subjected to unsparing scrutiny.

Johnson cycled through a series of press secretaries and cut back his interactions with journalists. White House aides convened a series of interagency groups, populated by top flacks from various departments and bureaus, to coordinate the administration’s war messages. But without real progress in Vietnam, nothing could change Johnson’s predicament.

And then there was Jimmy Carter. If Carter hadn’t presided over one of the most disastrous presidencies since Hoover’s, he might well have been remembered as a world-class image-maker like his successor, Ronald Reagan. But his public relations skills — hailed as unprecedented  when he first took office — were soon judged wanting as his policy fiascoes mounted.

During the 1976 presidential campaign, Carter, an obscure former governor from Georgia, capitalized on the post-Watergate mood of voter alienation to turn his anonymity into a virtue, his outsider status into an asset — and eventually to capture the presidency. Analysts attributed his success in good part to media wizardry, including his crack team of pollster Pat Caddell and advertising man Gerald Rafshoon.

They traded on Carter’s homespun, accessible style by “cutting back on ‘imperial’ frills and perks,” holding “fireside chats” to foster “personal intimacy with the people,” as Caddell prescribed in a memo. The media touted Carter’s image-making genius. A May 1977 New York Times Magazine cover showed a cartoon of the president, sporting a self-satisfied Cheshire-cat smile, operating a television studio console featuring multiple images of himself.

By 1978, however, Carter was groping about, trying to tame out-of-control unemployment, inflation and energy costs. Rafshoon, insisting that “all politics is marketing,” took over the Office of Communications. But now Caddell’s Everyman gimmicks — doing away with “Hail to the Chief,” having Carter wear cardigans — were faulted for depriving the president of the gravitas he needed to lead. The awe that reporters once held for Rafshoon curdled into ridicule. “Rafshoon” became a verb, meaning to market, or dress up in P.R. trappings: “Can Rafshooning Save the President?” The noun was “Rafshoonery” — as in buffoonery.

It’s rare that a president’s ills can be cured by altering his press strategy or changing up the communications office. The political consultant Paul Begala has quipped that “the Titanic had an iceberg problem. It did not have a communications problem.” Just so, Hoover’s misfortune was that he couldn’t spur recovery, Johnson’s that he couldn’t end the war, Carter’s that he couldn’t manage domestic or foreign affairs very well.

Likewise, Donald Trump is not likely to see his prospects rise by explaining himself better to the public. Instead, he needs to accumulate some achievements that voters care about.