"If I don't like you, I'll walk into the embassy and say I saw you talking to this Al Qaeda guy, or that I've heard you're talking about blowing up this airport," says Rick Nelson, a security expert at the Center for Strategic and International Studies.
In the past, such a warning might not have been sufficient to add the person's name to one of the watchlists maintained by the U.S. government, including the no-fly list and the selective-screening list. But President Obama announced last week he was ordering "an immediate effort to strengthen the criteria used to add individuals to our terrorist watchlists."
In the case of the accused Christmas bomber, the Obama Administration has never explained in detail why Umar Abdulmutallab was not put on a terrorist watch list after his father's November visit to the U.S. embassy in Nigeria. The White House review of the incident found that the failure to watchlist was a key error in the case, and said the watch list system "needs to be strengthened and improved."
There are signs that the decision not to watchlist Abdulmutallab was disputed even at the time: Newsweek reported that a CIA officer in Nigeria said after the visit Abdulmutallab should have been watchlisted.
A piece on CNN suggested that concerns about a poison pen may have contributed to the decision not to watchlist Abdulmutallab after his father's warning. Jill Dougherty reported that poison pens were one reason a person would not be watchlisted based on a single-source piece of information.
With the expected loosening of watchlisting standards, Nelson says we can expect to see expansion in the no-fly list (currently 4,000 names) and the selective screening list (14,000 names).