What year is it again?

Over the past few days, President Trump has been living in the year 2020, claiming that he defied his advisers to reopen the country during the coronavirus pandemic, saying that one of them, Dr. Anthony S. Fauci, was the one with all the “crazy ideas.”

He has revisited his near-daily falsehood that he won the 2020 election and that it was rigged, a belief held by a large swath of his political base. And, on Friday, he said that his supporters who ransacked the Capitol on Jan. 6, 2021, were simply on an “innocent journey.” Four people died that day.

Mr. Trump is not so much a student of history as a rewriter of it. In his second term, he is so set on avenging his election loss and pursuing retribution against his political enemies that he has Americans looking backward when many have signaled they would rather he explain why the country is at war with Iran, or help them afford groceries now, in the year 2026.

Neither his falling poll numbers nor the concerns among Republicans about the midterms seem to be modulating his insistence on revisiting much of what happened six years ago.

“I don’t think his ego allows him to accept the fact that someone he perceives as so weak as Joe Biden was able to beat him,” said Sarah Matthews, who was a deputy press secretary in the first Trump administration and resigned amid the Jan. 6 attacks.

“I witnessed it firsthand that he had advisers telling him he lost and there was no evidence of fraud,” said Ms. Matthews. “He stopped listening to those people and started surrounding himself with enablers and conspiracy theorists.”

Six years later, she said that Americans are still living with the consequences, “in the sense that he’s not focusing on the things that most Americans are focused on.”

In a statement, Abigail Jackson, a White House spokeswoman, suggested that Mr. Trump’s fixation on the 2020 election was part of an effort to pass the SAVE America Act, which would require voters to prove their citizenship to register, ban IDs without a photo at polling places and severely restrict voting by mail. Democrats have argued that the legislation would make it more difficult for eligible voters to make it to the polls.

“The president knows how critical this issue is for the American people, and he will not stop fighting until it is passed, but he can walk and chew gum at the same time,” she said. “The Trump administration continues to lower drug prices, restore American jobs, restore gold standard science and more.”

Last week, Senate Republicans joined Mr. Trump back in 2020. Revisiting a collective national trauma far more complicated than how they presented it, Senate Republicans trumpeted Dr. Fauci’s journal entries — recovered from a government server and shared with the public courtesy of Mr. Trump’s health secretary, Robert F. Kennedy Jr. In them, Dr. Fauci wrote of all the attention that he received from celebrities like Julia Roberts and Barbra Streisand.

Dr. Fauci invoked the Fifth Amendment over 100 times on Wednesday during a hearing before the Senate Homeland Security Committee. To many, this was a tacit admission of guilt from the 85-year-old, who retired from public service in 2022. (Mr. Trump pleaded the Fifth hundreds of times during a 2022 fraud trial, according to publicly available documents.)

In his journals, Dr. Fauci detailed his deteriorating relationship with Mr. Trump as they disagreed over experimental treatments for the virus, mask guidance, testing availability and school closures. There was tension as far back as January 2020, when the president was downplaying the spread of the mysterious virus.

“I had to answer that we are taking this very seriously and that Americans should not be frightened or worry,” Dr. Fauci wrote of a television appearance he made at the time. “Let us see if this pits me against the POTUS.”

Turns out, he was right to be wary: Mr. Trump has lumped Dr. Fauci in with a long list of political enemies he believes he made during the last year of his first term.

That list includes Joseph R. Biden Jr. Last month, Mr. Trump veered off course during events that were supposed to be about U.S. nuclear capability and manufacturing and the environment to insult his successor. He also claimed on social media that he had warned Mr. Biden about Dr. Fauci, despite the fact that Mr. Trump gave the doctor a presidential commendation for his work to bring a Covid vaccine to the public.

“I called Biden to tell him Fauci was no good, either didn’t have a clue, or was dishonest. The call was well received, but sadly, not acted on,” Mr. Trump wrote. “He went on to give Fauci vast destructive power.”

Two people directly familiar with Mr. Biden’s conversations with Mr. Trump, who were granted anonymity because they did not want to get into a public back-and-forth with the president, say that call did not happen.

A former senior administration official who was part of the first-term White House coronavirus task force and was granted anonymity to avoid getting into a public spat with former colleagues, recalled that Mr. Trump and his advisers would frequently disagree with Dr. Fauci in Situation Room meetings about the virus.

Dr. Fauci’s refrain during tense moments was to tell members of that group that his job was to make science-based recommendations. The job of White House officials, he said, was to weigh those recommendations against potential economic harm.

Mr. Trump’s retellings have, at a minimum, stripped nuance from matters as complex as his handling of a virus outbreak that would kill over a million people. In Mr. Trump’s version of events, there is only good and bad, hero and villain, with him or against.

Thomas B. Pepinsky, a political scientist and a co-author of “Pandemic Politics: The Deadly Toll of Partisanship in the Age of COVID,” said that this binary approach was evident during the pandemic and may have cost Mr. Trump the election he cannot stop obsessing about.

“The main finding was that the Trump administration interpreted the pandemic as a political threat,” Mr. Pepinsky, who teaches at Cornell, said of his research. “It was a tactical error. He could have been re-elected if he had treated the pandemic differently.”

Mr. Trump’s constant, incorrect assertions about the 2020 election results have carried a cost for American democracy. A raft of polls have found deepening distrust in government institutions and election security, but a partisan split in the reasons why. According to a Politico poll published in May, a majority of Republicans are worried about ineligible people voting, while a majority of Democrats are worried about voter suppression.

Many Americans remain legitimately angry and upset about what happened to them and their families during the pandemic. And experts like Mr. Pepinsky see a missed opportunity to learn from mistakes made in 2020.

Americans now face a growing measles outbreak and fears about food supply contamination. Asked last week about an outbreak of cyclosporiasis, a diarrhea-causing illness whose recent spread has been linked to contaminated iceberg lettuce, Mr. Trump shrugged off concerns.

“I haven’t thought about it,” Mr. Trump said, before joking with the reporter who asked the question. “Are you eating lettuce recently?”

People who know how Mr. Trump operates believe he will persist with his focus on the events of 2020, given the main lesson he seems to have learned from that time period: Facts have not gotten in the way of his opinions, and he has been rewarded for it.

“If he says something enough times, he has the world’s largest megaphone,” Ms. Matthews said. “Of course, there are going to be millions of Americans who are going to believe him and take him at his word, even if he has no evidence to back it up.”