The night featured attacks against Muslim Dems and tributes to Charlie Kirk.
The Trump campaign on Thursday fired off a letter to the U.S. Secret Service Director, claiming that attendees' safety is at risk as protesters plan to descend on the area.
Capitol Police said they temporarily locked down the headquarters of the Republican National Convention after a suspicious package with two vials of blood was found.
"While Barron is honored to have been chosen as a delegate by the Florida Republican Party, he regretfully declines due to prior commitments," the statement from the former first lady's office said.
Barron joins several other family members - Donald Trump Jr., Eric Trump and Tiffany Trump - who were also selected.
Republican committee members are calling it a "smart business decision," and expect more than 50,000 people to attend, bringing in an estimated $200 million to the city's economy.