The Secret Service was responding Tuesday night to an escalating protest that may have involved one or more smoke bombs being thrown over the White House fence.
An estimated 1,000 protesters have gathered. No arrests have been made, but authorities are on alert.
The Secret Service also deployed a robot to check out the devices on the North Lawn. No one is currently allowed to leave through the North Gate, but those with the right access can go through the White House and leave through the South Gate.
The Obamas were at dinner celebrating Michelle Obama's birthday, but they have since returned to the White House without difficulty.
The tense scene outside the White House follows an earlier protest on the West Lawn of the Capitol, in which several hundred protesters affiliated with the Occupy Wall Street movement decried the influence of corporate money in politics and voice myriad other grievances.
Organizers had touted the rally, known as Occupy Congress, as the largest national gathering of Occupy protesters to date and secured a permit that would have allowed up to 10,000 people to participate. By mid-afternoon, the protest appeared to have fallen far short of those goals.
Here's some video of this afternoon from Russia Today of a few hippies getting arrested.
Two differences from the Tea Party rallies on Capitol Hill---no one was arrested, and the crowd was much bigger.