1. The perimeter at the Washington Hilton

Interim D.C. Police Chief Jeffery Carroll said the suspect was likely staying at the hotel, which may have enabled access. Hotel was closed to the public from 2 p.m. ahead of the 8 p.m. event; protesters gathered outside in the rain. Around 2,300 guests underwent multiple security checks, including ticket verification and screening by Secret Service and TSA

2. Security measures inside the ballroom

Inside the ballroom for the dinner itself, there were further security measures.

The U.S. Secret Service maintained another perimeter around the President that included a buffer separating him and others seated at the head table from the rest of the attendees. Armoured plates were hidden under the table where Mr. Trump was seated. Secret Service agents were at their posts in front of the stage and in its wings, as were heavily armed counter-assault agents ready to respond to threats. Security details for dozens of other high-profile attendees were also in the ballroom.

3. Security overhauls and U.S. Secret Service training

After that Assassination attempt of Reagan at the Washington Hilton, the hotel built extensive security modifications specifically to accommodate the President, including a secured garage designed to fit the presidential limo, which leads to a dedicated elevator and staircase to ferry them to a secured suite reserved for their personal use.

-AP