When Justice Stephen G. Breyer was robbed in his Caribbean vacation home 10 days ago, the crime was unremarkable except for one fact: a machete-wielding intruder was able to walk right into the residence of one of the highest members of the United States government.

In an era when many top American officials are blanketed in security, Justice Breyer and his colleagues are the exceptions, freer but also more exposed than their counterparts in the executive and legislative branches.

Nowadays, it often seems that anyone who is anyone in Washington has a driver and a gaggle of taciturn protectors. Congressional leaders sweep into restaurants trailed by members of the Capitol Police; top White House advisers have Secret Service agents.

And every president is more heavily encircled than the one before. When President Obama wants to snorkel on his Hawaii vacations, the Secret Service clears the airspace above him, the shoreline in front of him and the water around him. An aide said Mr. Obama had even been surrounded by agents in wetsuits as he floated.