Beyond the riot, Jan. 6 was a dangerously close call. ABC News Chief Washington Correspondent Jonathan Karl asks: "What if Pence had followed Trump’s order? What would have happened if he had brought the gavel down during the joint session on Jan. 6 and thrown out Biden’s electoral votes in the states Trump had contested? What if he had declared Trump the winner of those states?"

J. Michael Luttig, a former federal appellate judge popular among conservatives, had advised Pence he would be violating the Constitution if he followed Trump’s order, and Luttig tells ABC News that if Pence had attempted to do it, he would have "plunged the country into a constitutional crisis of the highest order."

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-ABC News' chief Washington correspondent Jonathan Karl

As lawmakers returned the evening of Jan. 6 to certify the election following the attack, then-Vice President Mike Pence tweeted his thanks last year to the law enforcement officers who kept him safe, showing how he was rushed to a Capitol Hill parking garage during the attack.

In the subsequent weeks, video played at Trump’s second impeachment trial revealed just how close the rioters came -- some within 100 feet of Pence and his family, who were forced to take shelter in the Capitol.

In an interview with Trump for his book "Betrayal," ABC News Chief Washington Correspondent Jonathan Karl asked Trump at Mar-a-Lago last March if he was worried about the safety of his vice president.

"No, I thought he was well-protected," Trump said. "And I had heard that he was in good shape.”

When asked directly about the "’Hang Mike Pence’” chants on tape, Trump said, "Well, the people were very angry. Because it's -- it's common sense, Jon, it's common sense, that you're supposed to protect -- How can you, if you know a vote is fraudulent, right — how can you pass on a fraudulent vote to Congress?"

There is no evidence to support Trump’s claims that he won the election over Biden, despite dozens of failed court battles last year.

Senate Majority Leader Chuck Schumer, who is expected to appear with Pelosi at the day's events, has tied the anniversary to a push for voting rights legislation that the House passed last year but which is stalled in the Senate.

Voting rights will also be a portion of Biden’s speech, according to White House press secretary Jen Psaki.

More than a third of all restrictive voting laws enacted since 2011 were passed in 2021, according to an analysis by the Brennan Center for Justice.

At least 19 states enacted 34 laws restricting access to voting in 2021, as of Dec. 7. More than 440 bills with provisions that restrict voting access were introduced in 49 states in 2021, according to an analysis by the Brennan Center for Justice.

While Democrats take a lead on the day’s ceremonies, Republican leaders are not expected to be at the Capitol.

Senate Minority Leader Mitch McConnell is instead planning to attend the funeral of late GOP Sen. Johnny Isakson in Georgia. House Minority Leader Kevin McCarthy has repeatedly accused Democrats of politicizing the day after saying on Jan. 6, 2021, on the House floor that "President Trump bears responsibility" for the "attack on Congress by mob rioters."

Trump on Tuesday canceled a planned press conference for Thursday from Mar-a-Lago, while House Republicans will be at home "talking to their constituents about things that actually affect them" like inflation and high gas prices, according to a House Republican leadership aide.

-ABC News’ Benjamin Siegel