After nearly a dozen years of foiled plots, the United States on Monday suffered the first large-scale bombing since the attacks of Sept. 11, 2001, opened an era of heightened security affecting nearly every aspect of American life.
The disruption of those plots underscores the enormous strides that the American national security apparatus has taken, including the adoption of policies that remain the subject of intense concern among human rights and civil liberties groups.
But the success of the strike on the Boston Marathon, an international symbol of a city's pride, highlights the enduring difficulty that U.S. officials face in impeding a determined attacker.