One of three agents out with Naomi Biden on Sunday opened fire at people breaking a window of the unmarked Secret Service vehicle. No one was struck, officials said.
The independent presidential candidate urgently stepped up pressure for Secret Service help amid several looming threats cited by his campaign.
Right-wingers suggested that corruption was a factor after the probe failed to identity how the substance ended up inside the White House.
A preliminary test has shown that a suspicious substance found at the White House on Sunday was cocaine.
Authorities say a man crashed a U-Haul truck and began waving around a Nazi flag in the culmination of a six-month plan to “seize power” from the government.
The Secret Service confirmed Mayor Mohamed T. Khairullah was blocked from attending but did not provide any further details.
Older children have sometimes become stuck in the iconic barrier.
Rates the former president charged agents far exceeded the government's per diem, sometimes exceeding $1,000 a night per room.
Rep. Zoe Lofgren says the new evidence the panel has received contradicts aspects of the Secret Service members' previous testimony.
"Their plan is to literally kill people. Please, please take this tip seriously," one tipster said in a warning relayed to the Secret Service ahead of the attack.