Donald J. Trump’s ascent from New York City real-estate developer to the presidency was one of the most remarkable events in a generation, but apparently some aspects of his path to the White House didn’t leave much of an impression on Trump himself.

Trump said he either couldn’t remember, couldn’t recall or couldn’t recollect 36 times when answering questions about events during his campaign in written responses to Special Counsel Robert Mueller that were made public in the partially redacted report on Thursday.

“ Trump’s written responses didn’t allow for follow-up questions ‘that would ensure complete answers and potentially refresh your client’s recollection or clarify the extent of nature of his lack of recollection,’ Mueller’s team said. ”

Mueller’s report concluded that Trump’s campaign did not conspire with the Russian government, but it outlined 10 instances in which Trump may have obstructed justice.

Trump’s responses appear in Appendix C of the 448-page first volume of Mueller’s report, which outlined the results of the special counsel’s investigation into Russian interference in the 2016 presidential election. Investigators did not interview Trump face-to-face. Instead, they submitted dozens of questions to the White House that the president answered in writing and under oath.

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Trump’s alleged memory gaps go to the heart of key questions, including whether he was aware of Russian interference. In the written responses, Trump said he had “no recollection” of whether he knew that Russian president Vladimir Putin “supported” his candidacy and “opposed” his opponent Hillary Clinton and “no recollection” of whether he was told during the campaign that any foreign government or leader had provided or wished to provide support for his election effort.

He said he didn’t “recall being aware” of any communication between his campaign and WikiLeaks or other hackers, or whether he talked to Roger Stone about the release of hacked emails that were damaging to Clinton, or whether former Trump campaign chairman Paul Manafort communicated policy positions that Ukraine or Russia would want the U.S. to support.

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Trump also said he “had no recollection of learning at the time” that his son Donald Trump, Jr., Paul Manafort and Trump’s son-in-law Jared Kushner were planning to meet in June 2016 about potentially negative information about Clinton, the Democratic candidate for U.S. president.

Special counsel investigators were frustrated by Trump’s apparent memory lapses, the report reveals. Trump, through his lawyers, provided the written responses after Mueller’s team tried for more than a year to get Trump to sit down for an interview. When Trump finally submitted the answers, the special counsel’s office told Trump’s attorneys “of the insufficiency of those responses in several respects,” according to the report.

“We noted, among other things, that the President stated on more than 30 occasions that he ‘does not recall’ or ‘remember’ or have an ‘independent recollection’ of information called for by the questions. Other answers were ‘incomplete or imprecise,’” the report states. Mueller’s team added that written responses didn’t allow for follow-up questions “that would ensure complete answers and potentially refresh your client’s recollection or clarify the extent of nature of his lack of recollection.”

Mueller’s team asked again for a face-to-face interview, but Trump’s lawyers declined, according to the report. The special counsel considered a subpoena, but decided against it, partly because of the delay it would create and the “costs of potentially lengthy constitutional litigation.”

“ American history is littered with political leaders who have complained of weak memories when questioned about highly-scrutinized events that later ended up in history books. ”

Trump is hardly alone in claiming a fuzzy memory. American history is littered with political leaders who have complained of weak memories when questioned about highly-scrutinized events that later ended up in history books.

Bill Clinton testified that he had no memory of many aspects of his relationship with intern Monica Lewinsky, and Richard M. Nixon instructed White House counsel John Dean chief of staff H.R. Haldeman to say they couldn’t remember details of the Watergate scandal if they were asked to testify.

What events did make into Trump’s memory banks? He affirmed in his responses to Mueller that his onetime lawyer Michael Cohen suggested the possibility of a real-estate project in Moscow, and that the two had a few brief conversations on the topic that were “not memorable.”

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Trump also said he remembered winning Republican primaries in California, New Jersey, New Mexico, Montana and South Dakota, and he said he “generally recalls” making a victory speech on June 7, 2016.

Trump also recalled in detail a list of Clinton’s alleged shortcomings as a candidate, which he had planned to detail in a speech that was later rewritten after a shooting at the Pulse nightclub in Orlando, Fla. on June 12, 2016; the shooting at the gay nightclub left 50 people dead, including the perpetrator, Omar Mateen, a 29-year-old security guard.