WASHINGTON â€" The shoe bomber, the underwear bomber, and the Times Square bomber each failed in their primary objective, to kill Americans, but they contributed to a mood of both political resolve and deep worry about the country's terror defenses in the decade after 9/11.
Following the Boston Marathon attack, political leaders gave voice once again to those sentiments, but the reaction was magnified by the shocking toll, with the deaths of three people and widespread injuries from flying shrapnel.
Some politicians wondered whether the absence of a successful terrorist strike on US soil since Sept. 11, 2001, has lulled Americans into believing that all of the security screenings, intrusive searches, and ubiquitous surveillance cameras are keeping them safe â€" that they don't have to worry any more about every unattended backpack on the sidewalk.
''The complacency that prevailed prior to September 11 has actually returned," Senate Minority Leader Mitch McConnell, the Kentucky Republican, said in a speech on the Senate floor Tuesday morning. "And so we are newly reminded that serious threats to our way of life remain."
McConnell's assertion â€" part of a debate that for the moment has diverted attention from such issues as immigration and gun control â€" poses anew questions about how Americans respond to the threat of terror.
Have they grown so desensitized to the "if you see something, say something" warnings that they are less likely to say anything? Polls show terrorism has certainly faded as a public concern in the last dozen years since the 9/11 attacks.
''That's just human nature. And that's good. We don't want people obsessing about being afraid -- especially afraid of something that has a very, very low likelihood," said David Schanzer, a professor at Duke University who specializes in terrorism, Guantanamo Bay, and national security policy.
Former senator Joe Lieberman said the explosions in Boston brought to life "one of the nightmares" he had as a chairman of the Senate Committee on Homeland Security and Governmental Affairs: an attack on "relatively undefended massive events where there's a lot of people."
''The pain and insecurity that was brought on by the attacks of 9/11 naturally over time have diminished among the general public," the Connecticut independent said in an interview. "But I think people are still aware that we're living in a post 9/11 world. 1/8Monday3/8, tragically, brings it all back. It brings back the pain and the insecurity and the anger and the resolve not to let terrorism change our way of life."
President Obama said Tuesday investigators do not know whether the bombs that killed three and wounded scores at the Boston Marathon were an act of a single person or a an organized group -- or why they were planted.
But he struck a resolute note as he sought to reassure the country that the full force of US power and the justice system will be used to hunt down those responsible.
''American people refused to be terrorized," Obama said.