The Sept. 11 attacks prompted U. S. authorities to implement a rash of new rules aimed at preventing another act of terrorism from ever happening again.
Just two months later, shoe bomber Richard Reid attempted to blow up a jetliner by packing explosives in his shoes, which led airports to require passengers to remove their footwear while passing through airport security.
Now, nearly a decade later, U.S. authorities are implementing a whole new set of measures -- from patting down passengers from certain countries to implementing new screening technology -- meant to keep militants at bay.
But are the new rules making Americans any safer?
Some say yes. But for others, the answer is no. "I think the steps are just window dressing," said Scott Stewart, vice president of tactical intelligence at global intelligence company Stratfor.
The slew of new regulations was mandated in response to the Dec. 25 attempted bombing of a U.S.- bound jetliner by 23-year-old Nigerian national Umar Farouk Abdul Mutallab, who smuggled an explosive device on board in his underwear.
U.S. authorities have mandated that those carrying passports from 13 predominately Muslim countries plus Cuba -- and individuals traveling from or transiting through them -- are subject to full body pat downs, body scans and luggage and explosives checks.
But with Al Qaeda and its splinter groups constantly on the lookout for loopholes, some experts expressed doubt that the measures will prove effective, as radicals have been known to come from just about anywhere, from England to Belgium to the United States.
Indeed, four of the London subway bombers stemmed from nations other than the 14 listed nations and a Belgian woman in 2005 launched a suicide attack in Iraq.
"These guys adapt to security measures," Stewart said. "We've seen that time and time again."
"They have American operatives, they have European operatives. And Nigeria wouldn't be on this list if it weren't for the Christmas bombings," he said. "What's to stop them from using someone from, say, Togo?" Critics said the United States still has not learned that technology alone is no silver bullet for thwarting terror, as radicals will probe the
system until they find a weakness to exploit.
Politics also play into the Obama administration's decision, as the measure was put in place partially to prevent a public outcry, critics said.
Other experts said that while the president's measures are no panacea, they will have some impact.
Michael O'Hanlon, fellow at the Brookings Institution, said the steps should be viewed as ways to plug gaps.
"You don't think of it as preventing terrorism. That is unrealistic. You have to think of it as patching holes," he said. "But each time we see a bomber of this sort, we are more aware of what they are capable of and what we need to do."
Indeed, defending from terrorists is akin to a chess game in which militants seek to exploit weaknesses, which leads to U.S. countermoves.
Some technological solutions, including body imaging -- equipment that can see through clothing and detect hidden objects - - may be helpful in bomb detection, but may not find separate components that can be assembled
into an explosive device once the bomber is on board, he said.
In a speech on Tuesday, U.S. President Barack Obama outlined a number of general steps his administration will take, including new screening and security for all flights; more explosive detection teams at airports; more
air marshals on flights and deepening cooperation with international partners.
Counterterrorism officials have updated terrorist watch lists and added more individuals to the "no fly" list, while the State Department now requires U.S. embassies to include current visa information in warnings about those suspected of ties to militants.
"We have to do better -- and we will do better," said Obama of the administration's efforts to foil terror plots. "And we have to do it quickly. American lives are on the line."
To that end, the president also ordered a review of U.S. intelligence to determine why no action was taken in spite of knowledge of the Christmas bomber. While the U.S. Central Intelligence Agency possessed a report on the
Christmas bomber after his father alerted the U.S. embassy in Nigeria that his son had fallen in with a group of extremists, warnings were not heeded.
The investigation found that failures were not in collecting intelligence but in connecting and understanding the information various
agencies already had. Obama will direct intelligence agencies to more aggressively pursue
leads until plots are disrupted. Intelligence reports must be distributed more rapidly and the analysis process must be strengthened, he said in a security briefing on Thursday, his second in three days.
But while some expressed optimism over changes in intelligence gathering and deciphering, others were skeptical.
"It looks good on paper and would help, but the problem is making it happen in the real world," Stewart said.
Whatever further steps the administration takes, Stewart said any plans to set up yet another government bureaucracy would only further entangle intelligence agencies in a morass of red tape.
The Bush administration made that mistake when it created the massive Homeland Security Department in the wake of 9/11 -- instead of helping agencies share information, it slowed that process down, he said.
"With 9/11, there were balls dropped there, and we just keep making same mistakes over and over," he said.
"The bottom line is we just need people to talk to each other and act on information once they had it," he said. "With the Nigerian, no one wanted to make a decision to revoke his visa."