Not all that long ago, many Americans committed hours a day to tracking then-President Donald J. Trump’s every move. And then, sometime after the riot at the Capitol on Jan. 6, 2021, and before his first indictment, they largely stopped.

They are having trouble remembering it all again.

More than three years of distance from the daily onslaught has faded, changed — and in some cases, warped — Americans’ memories of events that at the time felt searing. Polling suggests voters’ views on Mr. Trump’s policies and his presidency have improved in the rearview mirror. In interviews, voters often have a hazy recall of one of the most tumultuous periods in modern politics. Social scientists say that’s unsurprising. In an era of hyper-partisanship, there’s little agreed-upon collective memory, even about events that played out in public.

But as Mr. Trump pursues a return to power, the question of what exactly voters remember has rarely been more important. While Mr. Trump is staking his campaign on a nostalgia for a time not so long ago, Mr. Biden’s campaign is counting on voters to refocus on Mr. Trump, hoping they will recall why they denied him a second term.

“Remember how you felt the day after Donald Trump was elected president in 2016,” the Biden campaign wrote in a fund-raising appeal last month. “Remember walking around in disbelief and fear of what was to come.”

For now, the erosion of time appears to be working in Mr. Trump’s favor, as swing voters base their support on their feelings about the present, not the past. A New York Times/Siena College poll conducted late last month found 10 percent of Mr. Biden’s 2020 voters now say they support Mr. Trump, while virtually none of Mr. Trump’s voters had flipped to Mr. Biden. The poll found Mr. Trump’s policies were viewed far more favorably than Mr. Biden’s.