Former FBI director James B. Comey, left, is a frequent target of criticism by President Trump. (Nicholas Kamm/AFP/Getty Images)

In its 110 years, the FBI has weathered storm and scandal. It has had moments that make Americans proud of its crime-fighting and anti-terrorist activities. Yet its most celebrated and longest-serving leader, J. Edgar Hoover, for whom the imposing headquarters on Pennsylvania Avenue is named, is remembered in large part for the abuses of power that took place during his reign.

What is occurring today is different. It is more like the crumbling of the foundations of an agency that on its best days personifies the finest in government service and law enforcement. Like much about today’s political environment, the problems began before President Trump was elected but have become far worse during his time in office.

There can be no strong foundation at the FBI when the pillars of leadership are all under assault, starting at the very top — the Justice Department. Attorney General Jeff Sessions recused himself from overseeing special counsel Robert S. Mueller III’s investigation into Russian interference in the 2016 election, possible collusion by Trump campaign associations and now much more. Sessions’s recusal is, in Trump’s eyes, the original sin for which he has never forgiven the former senator.

Sessions not only is a bystander to the Russia probe and but also has been weakened by constant disparagement that comes from the Oval Office. His precarious position, despite occasional instances of pushing back, undermines what should be the Justice Department’s independence from the White House. The president has sought to cripple the chief law enforcement official in the government and, with it, the department.

Sessions’s deputy, Rod J. Rosenstein, a career prosecutor, has no job security either. It was he, after Sessions’s recusal, who decided to appoint a special counsel and hand the Russia investigation to Mueller. The wrath the president expresses toward Sessions has been transferred to Rosenstein, though it was Rosenstein who was asked to provide the memo that formed the pretext for the of then-FBI director James B. Comey.

Rosenstein’s ability to manage and lead has been compromised by the president. Now, the president’s allies in Congress have joined in applying pressure on him. He retains his job, despite constant talk that he could be fired, but he must walk into the building each day and wonder if it will be his last on the job. There is one positive sign amid all this: The Post reported Friday that Sessions has warned that he might leave his post if Rosenstein is fired.

Comey’s tour promoting his new book, “A Higher Loyalty: Truth, Lies and Leadership,” highlights the degree to which the tables have turned, both for him and…