The prospect of more of the U.S. capital being closed off after an intruder got into the White House has struck a nerve in Washington, where ever more public space is being eroded by barricades and bollards.

The possible tightening of security around the president's residence, a highly visible symbol of democracy and a prime draw for tourists and protesters alike, raises questions such as whether safety trumps openness or whether a capital city can ever be entirely safe.

The week after a 42-year-old Iraq war veteran climbed the wrought-iron fence around the White House, sprinted across the lawn with a knife in his pocket and entered the executive mansion through an open door, law enforcement officials erected a second fence around parts of the White House.