Robert Mueller defended his Russia investigation against criticism from former special counsel prosecutor Andrew Weissmann and others, arguing that he ran the effort “without any interest in currying favor or fear of the consequences."

The 76-year-old former FBI director, who has only spoken out about the Russia investigation one other time since testifying before Congress last summer, also said he stood by his team members and his report.

“It is not surprising that members of the Special Counsel’s Office did not always agree, but it is disappointing to hear criticism of our team based on incomplete information,” Mueller said in a rare public statement first obtained by the Washington Post.

“When important decisions had to be made, I made them. I did so as I have always done, without any interest in currying favor or fear of the consequences. I stand by those decisions and by the conclusions of our investigation," Mueller said. The former special counsel also his team knew “that our work would be scrutinized from all sides,” but he believed they made the correct calls.

Weissmann has a new book out on Tuesday in which he criticized aspects of the special counsel investigation.

“Had we given it our all — had we used all available tools to uncover the truth, undeterred by the onslaught of the president’s unique powers to undermine our efforts?” Weissmann, who became known as Mueller's "pit bull," wrote in Where Law Ends. “I know the hard answer to that simple question: We could have done more.”

Weissmann, now an MSNBC analyst who is being scrutinized for wiping data from two government-issued phones while on the Mueller team, told the Atlantic that the former special counsel “absolutely” let people down.

“I wouldn’t phrase it as just Mueller," Weissmann said. "I would say ‘the office.’ There are a lot of things we did well and a lot of things we could have done better.” He added that “like Congress, we were guilty of not pressing as hard as we could."

Weissmann’s book trashes two major decisions. One is Mueller choosing not to subpoena Trump to testify and the other is Mueller's report not reaching a decision on whether Trump obstructed justice.

He laid some blame for what he viewed to be the Mueller investigation’s failures at the feet of another prosecutor, Aaron Zebley. Weissmann compared Zebley to George McClellan, a general for the Union during the Civil War who was removed from command by President Abraham Lincoln, and himself and others to Gen. Ulysses S. Grant, who led the Union to victory over the Confederacy. Weissmann claimed that “repeatedly during our twenty-two months in operation we would reach some critical juncture in our investigation only to have Aaron say that we could not take a particular action because it risked aggravating the president beyond some undefined breaking point.”

Mueller defended Zebley on Tuesday as “an invaluable and trusted counselor to me from start to finish” and said he “selected him for that role because I knew from our ten years working together that he is meticulous and principled.” Mueller argued that Zebley was “privy to the full scope of the investigation and all that was at issue” and that he did a good job.

Mueller also explained his decision not to issue a Trump subpoena in testimony before the House Judiciary Committee in July 2019.

“At the outset, after we took over the investigation and began it, pursued it, quite obviously, one of the things we anticipated wanting to accomplish was having the interview of the president. … We negotiated with him for a little over a year,” Mueller said. “Finally, we were almost towards the end of our investigation, and we'd had little success in pushing to get the interview of the president. We decided that we did not want to exercise the subpoena powers because of the necessity of expediting the end of the investigation.” Trump answered questions in writing.

Weissmann claims in his book that “the explanation that the legal battle would have unduly delayed the inquiry was less than candid, since a subpoena issued at the start of the investigation could have been resolved by the Supreme Court months before the date of the report’s completion,” according to the Atlantic. “Weissmann reveals that the real reason for not compelling the president to be interviewed was Mueller’s aversion to having an explosive confrontation with the White House.”

Mueller’s April 2019 report noted that “we determined not to apply an approach that could potentially result in a judgment that the President committed crimes,” but it laid out 10 possible instances of obstruction by Trump, including aborted efforts to remove Mueller.

“If we had confidence after a thorough investigation of the facts that the President clearly did not commit obstruction of justice, we would so state. Based on the facts and the applicable legal standards, however, we are unable to reach that judgment,” Mueller’s report concluded. "While this report does not conclude that the President committed a crime, it also does not exonerate him.”

Weissmann wrote in his book that he was "flummoxed by Mueller’s thinking" and claimed that “part of the reason the president and his enablers were able to spin the report was that we had left the playing field open for them to do so.”

A letter written by Attorney General William Barr in March after he received Mueller’s report but prior to its release said the special counsel did not draw a conclusion "one way or the other" on the issue of obstruction of justice. Barr quoted Mueller’s report as saying that “while this report does not conclude that the President committed a crime, it also does not exonerate him.” Barr said he and Deputy Attorney General Rod Rosenstein concluded that it was not sufficient to establish criminality.

Weissmann’s book claims that “Barr had betrayed both friend and country.”