Nearly 200,000 flags are on display, representing the American people unable to attend.
Some 25,000 National Guard troops from around the country were due in the District of Columbia in the coming days.
The president's followers brought chaos to the U.S. Capitol after his speech at the National Mall.
Advocates have pushed for the museum since 1994, when a task force found the Smithsonian had "willfully neglected" Latinx people in its programming.
The president, who was not wearing a mask, claimed without evidence that 99% of U.S. coronavirus cases are "totally harmless" at the National Mall event.
The administration is holding the event again this year, despite coronavirus concerns.
“Most likely we’ll be standing 6 feet apart” in a “very, very interesting way," the president said last month.
News of Glenna Goodacre's death was posted to Instagram by Harry Connick Jr., who is married to her daughter, Jill Connick.
He is the first president to address the annual rally against abortion rights in person, according to the event's organizers.
The National Park Service backed down from its plan to severely limit protests near the White House and National Mall after a wave of bipartisan outrage.