On Wednesday, the Secret Service will take command of security preparations at the U.S. Capitol and other federal buildings, backed by as many as 15,000 National Guard troops, thousands of police and tactical officers, and layers of eight-foot steel fencing.

The high-alert security posture is starting six days earlier than planned to coordinate roles for the FBI, National Guard, U.S. Marshals Service and a host of other federal agencies that will fall under Secret Service command.

“Everyone can just rest assured they are throwing the kitchen sink at this event,” said one Secret Service official involved in protective planning who was not authorized to speak to reporters…

Veteran Secret Service and Homeland Security officials who spoke on the condition of anonymity to share their worries described a level of concern unlike anything in their careers. Threats they fear include a plot by armed groups to encircle the White House or the U.S. Capitol and the inauguration event, as well as the possibility that gunmen could stage coordinated attacks against less-fortified targets in the city.