Government agencies, airport screeners and airlines are taking much closer looks -- again -- at who's allowed to board planes in the United States or aircraft heading here. This latest terrorism alert follows federal charges against a Nigerian passenger accused of trying to blow up a Northwest Airlines plane approaching Detroit's airport on Christmas morning. President Obama says the 23-year-old African man was on a mission for Al Qaeda, the radical Islamic group that attacked America on Sept. 11, 2001.

This time, plenty of clues about accused bomb-carrier Umar Abdulmutallab were missed. Britain refused to renew his student visa last May and put him on a watch list. In August, the U.S. National Security Agency overheard Al Qaeda leaders in Yemen (a Mideast nation) discussing a plot involving a Nigerian man. In November, the suspect's dad warned a CIA agent at the U.S. Embassy in Nigeria that his son was being radicalized and had disappeared in Yemen. Then the would-be bomber paid cash for a ticket to Detroit and boarded his ocean-crossing flight with just a carry-on bag -- acts that should trigger close scrutiny, security experts say.

Obama acknowledged "a systemic failure has occurred" and ordered reviews of the federal terrorist watch list system, air travel screening and information-sharing among security agencies. Starting this week, U.S.-bound fliers from Saudi Arabia, Nigeria, Yemen and other "countries of interest" are undergoing full body scans or pat-downs, explosive detection screening and a close search of carry-on luggage.
The near-tragedy adds urgency to a debate over body scanners that reveal objects hidden under clothes at airport checkpoints, as shown in the video below. That technology would have detected an explosive chemical packet in the Nigerian man's underpants, anti-terrorism specialists say. But privacy advocates say it's too intrusive to let screeners see detailed body outlines, which critics call "a digital strip search." Congressman Jason Chaffetz, R-Utah, says: "I don't think anybody needs to see my 8-year-old naked in order to secure [an] airplane."

President says: "As the Christmas Day attempt illustrates . . . the hard work of protecting our nation is never done. So as our reviews continue, let us ask the questions that need to be asked. Let us make the changes that need to be made. Let us debate the best way to protect the country." -- Jan. 2 radio address

Ex-vice president says: "We are at war and when President Obama pretends we aren't, it makes us less safe. Why doesn't he want to admit we're at war?" -- Dick Cheney, 2001-09 Republican vice-president, commenting last week

Air traveler says: "It seems that nothing at all was learned from 9/11. We, the passengers, are still paying the price for governments' and airlines' sheer stupidity." -- Caryl Baron of Sandia Park, N.M.