Three years later, Jan. 6 hangs over the presidential contest.

Saturday is the third anniversary of the Jan. 6 attack on the Capitol. The consequences of that fateful day still reverberate through American politics, and its fallout looms intensely over the 2024 presidential race.

While former President Donald J. Trump holds a commanding lead in polls on the Republican Party’s nominating contest, he is facing 91 felony counts in four separate cases, two of which spring from his attempts to overturn the 2020 election, which culminated on Jan. 6.

He is joining the campaign trail on Friday in Iowa, a state his challengers have been stampeding across before the caucuses on Jan. 15. Gov. Ron DeSantis of Florida and former Gov. Nikki Haley of South Carolina held dueling CNN town halls there on Thursday night.

President Biden, gearing up for a likely rematch from 2020 against the man who still denies the outcome, is heading to Pennsylvania on Friday to make his re-election pitch in a speech drawing attention to the events of Jan. 6 and the role Mr. Trump’s election denialism played in stoking the violence.

Mr. Biden is seeking to reunite a sprawling anti-Trump coalition that led him to victory in 2020 and blunted what was predicted to be a “red wave” midterm election in 2022. Highlighting Mr. Trump’s most divisive qualities will be central to that strategy.

But the incumbent is facing strong headwinds when it comes to his own popularity. Gallup polls have shown Mr. Biden’s approval rating below 40 percent since October, driven in part by economic discomfort and two foreign wars in Ukraine and Gaza that Americans have mixed feelings about being involved in — even indirectly. A New York Times/Siena College poll from November showed Mr. Biden losing to Mr. Trump in five of six key battleground states.

In his first campaign event of the year, Mr. Biden will frame the 2024 election as an existential battle for American democracy. The site of the speech holds symbolic importance: The president will discuss the state of American democracy near Valley Forge, where American revolutionaries, led by George Washington, survived a harsh winter and emerged as a more potent fighting force.

Mr. Trump, for his part, is just as eager to draw attention to the events of Jan 6. He continues to falsely claim that the 2020 election was stolen from him, a refrain of the rallying cry he gave to supporters that day when he told them to “fight like hell,” otherwise “you’re not going to have a country anymore.”

In other news

• Gov. Kristi Noem of South Dakota, an ally of Mr. Trump who has been campaigning on his behalf in Iowa, told an NBC reporter that she would consider being his vice-presidential running mate.

• Two groups of voters in Massachusetts and Illinois filed challenges to Mr. Trump’s ballot eligibility in those states. The voters in both states are working with the same group, Free Speech for People.

• A political action committee controlled by Gov. Ron DeSantis of Florida donated $92,500 to 14 Iowa legislators who have endorsed his candidacy for president.

• A school shooting in Perry, Iowa, on Thursday killed a sixth-grade student and injured five other people. Vivek Ramaswamy, the entrepreneur running for president, was campaigning in Perry that day and led a prayer circle there. Mr. DeSantis suggested in an interview that he did not support changing federal law to prevent such shootings, telling NBC News it was “more of a local and state issue.”

Jonathan Swan, Maggie Astor, Nicholas Nehamas and Molly Longman contributed reporting.