A centuries-old norm has been broken. The inauguration of Joe Biden and Kamala Harris will not mark the peaceful transition of power. On Wednesday, American carnage arrived. Five people including a police officer are dead.

Yet even as the halls of Congress shuddered, the will of the people prevailed. Institutions held. How much longer is the unanswered question.

Against this Boschian landscape, James Comey again chronicles the destructiveness of Donald Trump. Like A Higher Loyalty, Comey’s first book, Saving Justice offers a defence of the FBI and the Department of Justice while tracking the author’s own career and lashing the 45th president.

For the FBI director Trump fired, the president’s gaze was akin to the Eye of Sauron in Tolkien’s Lord of the Rings trilogy. Fiery, malevolent, unblinking and consumed with self.

Saving Justice is perhaps already yesterday’s news. Two Trump cabinet officers have resigned, including Senator Mitch McConnell’s wife, Elaine Chao, from transportation. Larry Hogan, the Republican governor of Maryland, has called for Trump’s removal. Bill Barr, Trump’s second attorney general, has accused his former boss of betraying his office. The transition has become a national nightmare.

Comey’s book is paean to America’s institutions at a time when they need reinforcement. But whether Comey is the ideal messenger is another story. Since the presidency of George W Bush, he has repeatedly found himself in the spotlight, his judgment under attack.

As related by Fight House, a chronicle of internal White House skirmishes written by Tevi Troy, who served under the second President Bush, Comey sought to justify himself in a clash with Vice-President Dick Cheney over government surveillance, saying “the time to be a jerk was now” – not the most adroit choice of words. Likewise, his handling of Hillary Clinton’s email use remains a gaping wound.

Still, it is worth hearing Comey out. Saving Justice makes a heartfelt case for fealty to the rule of law and the constitution. Such lessons demand repetition.

Comey relays how as a young prosecutor, his supervisor directed him to advise a court of potentially exculpatory information. The case had already gone to the jury. That Comey thought the facts in question minor was not dispositive. The appearance of fairness mattered.

As Comey saw it, “One of things that has been right with American justice is the reality and reputation built” by the DoJ. He takes particular pride in its role in civil rights enforcement.

Comey’s insights into Barr and Rudy Giuliani, Trump’s consigliere, are noteworthy. Comey worked for Giuliani in the US attorney’s office in Manhattan. Decades later, he would possess front-row seats to Barr’s debasement and abuse of power. Comey knows of who and what he speaks.

Saving Justice recounts early interactions with New York’s future mayor in a case involving drug evidence gone missing. Asked by Giuliani what had happened to the contraband, Comey answered honestly. He did not know. Writing of how he was directed to draft an affidavit attesting to that fact, he recalls his fear: “I could type but no longer swallow.”

Saving Justice provides a key confession. It took Comey “years to realize that a leadership culture focused entirely on the boss was not a healthy one” and this is “something the entire country would learn when Rudy’s friend, Donald Trump, became president”. Giuliani now reportedly seeks a presidential pardon.

As for Barr, Comey takes aim at his distortion of Robert Mueller’s report on Russian election interference and links between Trump and Moscow; his intervention in the prosecutions of Michael Flynn and Roger Stone; and his subservience to the president, which lasted until the end of Trump’s time in office. Comey casts Barr as having betrayed what the DoJ was and should again become.

Comey recalls how Barr earned the ire of the federal judiciary. Last year, Judge Reggie Walton, a George W Bush appointee, “seriously” questioned the credibility and integrity of the attorney general. Assessing Barr’s handling of the Mueller report, Walton deployed words like “distorted” and “misleading”.

It didn’t end there. John Gleeson, a former federal judge appointed to review the decision to drop the Flynn case, leveled similar charges. Gleeson repeatedly resorted to the word “corrupt” and accused the government of “gross abuse of prosecutorial power”. Trump’s pardon of Flynn followed.

Barr has now abandoned Trump. In the run-up to invasion of the Capitol, Trump lamented that he still “likes” Barr, but regretted that Jeff Sessions’ replacement “changed because he didn’t want to be considered my personal attorney”. These days, only the conspiracy theorist Sidney Powell appears eager to do so.

Hoping to turn the page, Comey opposes federal prosecution of Trump. But he leaves the door open to state and local authorities pursuing him after he leaves the presidency. As for Joe Biden’s attorney general, he recommends someone “above the partisan scrum”.

From the look of things, Judge Merrick Garland fits that bill. Already, his selection has won the approval of Lindsey Graham, outgoing chair of the Senate judiciary committee.

“He is a man of great character, integrity and tremendous competency in the law,” Graham said.

A reminder: Senate Republicans under McConnell, including Graham, blocked consideration of Garland as a supreme court justice.

The impact of Saving Justice is likely to be limited. Events have overtaken its message. When Trump has lost Rupert Murdoch’s Wall Street Journal, the end is near.

But only in part. Trump has recast his party in his own image. More than two-thirds of Republicans did not consider storming the Capitol a threat to democracy. A plurality actually supported the putsch. Abraham Lincoln’s admonition against a house divided springs readily to mind.

Elite opinion carries limited sway. Americans continue to retreat into their bubbles. Much as Comey wishes, wide-scale institutional trust will not soon be restored. As for normalcy returning to Main Justice? We can hope.

• Saving Justice: Truth, Transparency and Trust, is published in the US by Flatiron Books and Macmillan in the UK.