WASHINGTON — It was supposed to be the largest Fourth of July celebration in recent history, featuring a record-breaking fireworks display and remarks by President Donald Trump.

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But despite Trump’s best efforts, the weather stymied his plans, forcing thousands of spectators to evacuate as lightning and dark clouds rolled over the White House toward the celebration area surrounding the Washington Monument.

Shortly after the main program was set to begin, organizers announced spectators needed to evacuate. Saturday’s evacuation was the latest instance of weather emergencies forcing officials to alter or cancel long-planned programming to commemorate the nation’s 250th anniversary.

Thousands of attendees, many of whom waited for hours in the searing heat, were directed to seek shelter in buildings near the National Mall, including the African American History Museum and the Ronald Reagan Building. Many appeared reluctant to leave until security officials urged them to evacuate.

As attendees streamed toward the exits, jets completed flyovers overhead.

Inside the Ronald Reagan Building, National Guard troops set up seats for spectators clad in red, white and blue and provided free water.

In the hours before the program was set to kick off, spectators reckoned with a triple digit heat index, with multiple people telling NBC News they witnessed others pass out or experience medical issues.

It is unclear whether Saturday’s event is expected to resume.

The Fourth of July programming comes amid a weekslong celebration on the National Mall, which was hit with spiking temperatures that forced officials to temporarily shut down the Great American State Fair. Health officials had more than four dozen patient contacts at the program, according to the D.C. Fire Department.

The Fourth of July event is spearheaded by Freedom 250, the public-private partnership established by the Trump administration. Another group, America250, is a non-profit established a decade ago to commemorate the 250th anniversary of the U.S. but is not affiliated with the Freedom 250 Fourth of July program.

Freedom 250 and the National Park Service planned to launch about 850,000 fireworks across several D.C.-area locations, which would have set a new record for the largest fireworks display. The previous Guinness World Record was set in 2016 in the Philippines, where 811,000 fireworks were launched at a megachurch. Those record-setting fireworks were launched over the course of an hour, but Freedom 250 planned to set off the July 4 fireworks during a 40-minute show.

The fireworks had been expected to dwarf typical July 4 shows, which usually consist of about 33,000 fireworks during a 20 minute show. Saturday’s show will feature more than 25 times the typical number of fireworks.

In May, several performers announced that they would no longer perform throughout the weeks-long program, despite having been listed on the lineup. Multiple artists cited the events’ politics in explaining their decision. Days later, Trump slammed the artists and suggested canceling performances.