Former acting FBI director Andrew McCabe, seen testifying on Capitol Hill in 2017, is promoting his book, “The Threat.” (Melina Mara/The Washington Post)

President Trump has called former FBI acting director Andrew McCabe a liar, a disgrace to the country and, on Wednesday, “a poor man’s J. Edgar Hoover” — the latest example of efforts by the president and his supporters to undercut the credibility of an impending report on Russian interference in the 2016 election.

The attacks on McCabe in particular serve a dual, if internally contradictory, purpose for Trump: to discredit McCabe’s highly critical new book while using it to advance a case that he is the victim of a corrupt “deep state” plotting an administrative coup.

As McCabe promotes his book, “The Threat,” in media interviews, Trump and his conservative allies have seized on assertions that McCabe and Deputy Attorney General Rod J. Rosenstein discussed options for invoking the Constitution’s 25th Amendment to oust the president in 2017. While casting aside McCabe’s other allegations as lies, Trump has sought to cite parts of the unflattering book as evidence to his political base that his presidency is under siege by unelected bureaucrats.

“Wow, so many lies by now disgraced acting FBI Director Andrew McCabe. He was fired for lying, and now his story gets even more deranged,” Trump wrote Monday on Twitter. “He and Rod Rosenstein, who was hired by Jeff Sessions (another beauty), look like they were planning a very illegal act, and got caught.”

The escalating attacks and tweets targeting McCabe and other investigators have set the stage for an even more aggressive onslaught from Trump and his conservative allies once special counsel Robert S. Mueller III completes his investigation into Russian election interference and possible obstruction of justice by the president. Mueller could submit his findings to Attorney General William P. Barr as early as next week.

“As a base play, it certainly makes sense to be talking about the deep state,” said Doug Heye, a former spokesman for the House leadership and the Republican National Committee. “That fits right into what the base already wants to believe about people in the administration trying to thwart Trump at every instance.”

McCabe is the latest official to draw Trump’s ire as federal investigators and congressional Democrats probe almost every facet of his life and he gears up to run for reelection.

“I think Andrew McCabe has made a fool out of himself over the last couple of days,” Trump told reporters Wednesday. “I think he’s a disaster and what he was trying to do was terrible, and he was caught. I’m very proud to say we caught him.”

McCabe said in response on MSNBC: “You think someday you’ll get used to this, and on some level, you never do. I’ve been listening to the president lie about me since October of 2016, and he somehow finds new ways to do it.”

On Tuesday, counselor to the president Kellyanne Conway alternated between calling McCabe a liar and saying his assertions about the 25th Amendment discussions were tantamount to a failed coup attempt. She predicted Trump would be reelected to a second term, despite his legal troubles.

“Andrew McCabe tried to overthrow a democratically elected president,” Conway said on CNN’s “Cuomo Prime Time.” “Hey folks, Donald Trump’s the president. It’s been going on for a couple years now, and get used to it because it’s going to last another six.”

While Trump has long been critical of McCabe, who became acting FBI director after Trump fired James B. Comey in May 2017, his attacks have escalated this week in the wake of McCabe’s book release and media tour. The president has interspersed his attacks on McCabe with missives targeting Mueller, attempting to draw a link between the two men who have investigated his possible ties to Russia.

“The Mueller investigation is totally conflicted, illegal and rigged!” Trump tweeted on Sunday. “Should never have been allowed to begin.”

In a “60 Minutes” interview that aired Sunday, McCabe revealed the critical role he played in moving forward the investigation into whether the Trump campaign conspired with Russia during the 2016 election. In the days after Comey was fired, McCabe authorized opening an investigation into Trump personally — a case that would explore whether Comey’s firing was an attempt to obstruct justice and whether Trump himself was compromised by the Kremlin. McCabe moved so quickly to initiate the case that some at the Justice Department were initially concerned he might have acted out of a desire for vengeance over Comey’s firing, people familiar with the matter, who spoke on the condition of anonymity, have said.

McCabe himself was ultimately fired from the FBI in March 2018, after the Justice Department inspector general found he had lied four times to investigators exploring a media disclosure about cases related to Hillary Clinton. McCabe has alleged that his firing was politically motivated — retaliation, he claims, for his opening the case against Trump. But the evidence the inspector general laid out was so damaging that it convinced federal prosecutors to open a criminal investigation into the matter using a grand jury. That case is ongoing.

Trump and his allies have seized on the IG’s report to dismiss McCabe as a liar. But as McCabe has gone on a media blitz to promote his book — doing more than a dozen television and radio hits in recent days, including on “The View,” as well as “The Late Show With Stephen Colbert” and “Morning Joe” — the president and his allies have tied themselves into something of a logical knot.

While Trump and his defenders have continued to term ­McCabe a fabulist, they have accepted as fact his description of conversations with Rosenstein, in which he alleges Rosenstein suggested wearing a wire to surreptitiously monitor the president and broached the idea of Cabinet members using the 25th Amendment to remove him.

By labeling McCabe a “poor man’s J. Edgar Hoover” on Wednesday, Trump also evoked images of the controversial former FBI director who used the bureau’s powers to spy on political activists.

Rosenstein has said he disputes McCabe’s account, though his carefully worded statements do not make clear what he claims actually happened. Trump said Tuesday he planned to nominate Jeffrey Rosen, a longtime litigator and deputy transportation secretary, to replace Rosenstein if and when he steps down.

In his recent interviews, Mc­Cabe has offered a bevy of information likely to inflame the president. He told Savannah Guthrie on Tuesday on NBC’s “Today” that the FBI worried “the president himself might, in fact, be a threat to the United States’ national security,” then later told CNN’s Anderson Cooper it was “possible” the president was a Russian asset. But McCabe has also been pressed to respond to the president’s stream of criticism.

McCabe’s book, which describes Trump as a threat to democracy, is the latest insider account to draw angry tweets from the president. Trump has given free publicity to tell-alls by Comey, former White House aides Cliff Sims and Omarosa Manigault, and others.

By tweeting and talking about McCabe, Trump is amplifying the book’s message, Heye said.

“Nobody sells more anti-Trump books than Donald Trump and his Twitter feed,” he said.