That's based on a Secret Service email from 9:09 a.m.
"The head of the President’s Secret Service protective detail, Robert Engel, was specifically aware of the large crowds outside the magnetometers," Schiff said.
A Secret Service report at 7:58 a.m. said, "Some members of the crowd are wearing ballistic helmets, body armor carrying radio equipment and military grade backpacks."
On Dec. 26, a Secret Service field office relayed a tip that had been received by the FBI, Schiff said.
Trump would not be the first president to be subpoenaed, nor would he be the first former president subpoenaed by Congress.