JUDY WOODRUFF: The U.S. Senate took a hard look at airport safety today and two new accounts questioning the effectiveness of the Transportation Security Administration.

MAN: This Senate hearing will come to order.

JUDY WOODRUFF: The Senate hearing came a week after the leak of a damning report on the TSA's failures. The federal Department of Homeland Security, TSA's parent agency, found fake explosives, weapons and other banned items went unnoticed in 67 of 70 tests.

Today, Nebraska Republican Senator Ben Sasse questioned John Roth, the inspector general who wrote the report.

SEN. BEN SASSE, R-Neb.: Do you think it's possible that TSA really could really have not understood how grave their problem was before last week's leaked report?

JOHN ROTH, Inspector General, Department of Homeland Security: You know, it's something that we think about all the time. I mean, do they truly understand the nature of the risk that they face? Candidly, I worry about that.

JUDY WOODRUFF: Others said they're worried that a push for reduced airport wait times has actually harmed security.

Rebecca Roering is assistant TSA director at the Minneapolis-St. Paul Airport.

REBECCA ROERING, Assistant Federal Security Director, Minneapolis-St. Paul International Airport: TSA is handing out pre-check status like Halloween candy in an effort to expedite passengers as quickly as possible, despite self-admitted security gaps that are being created by the process.

JUDY WOODRUFF: Meanwhile, a second inspector general's report finds TSA's vetting of aviation workers is — quote — “generally effective.” But it did fail to identify 73 employees with unspecified links to terrorism.

For all that, at today's hearing, Missouri Democrat Claire McCaskill offered a partial defense of the security agency.

SEN. CLAIRE MCCASKILL, D-Mo.: We have got to remember, as we all sit and pound the desk about how bad TSA is, we keep cutting the amount of money they have. And we ask them to do more and do it better.

JUDY WOODRUFF: The hearing was cut short after a telephoned bomb threat that turned out to be a hoax.

And joining me is Jack Riley. He's vice president of the RAND Corporation's National Security Division. He focuses on transportation and border security.

Mr. Riley, thank you for being with us.

How concerned should the American people be? These lapses sound pretty serious.

JACK RILEY, RAND National Security Research Division: Well, I understand why the reports are alarming, but I think the thing people need to keep in mind is that there are a number of other layers that are in place to help keep planes safe, not the least of which is cockpit doors are locked, passengers and crew know that they have to intervene, and on many flights, an unknown percentage, but many flights, we have air marshals present.

So there are a lot of other layers to security. And focusing simply on one segment I think is a disservice.

JUDY WOODRUFF: So when they say that out of a test, 67 out of 70 contraband items, they said, got through undetected by TSA, that doesn't sound concerning?

JACK RILEY: Oh, no question that it's an abysmal performance, but the average TSA person during the course of a week probably encounters thousands, if not tens of thousands of passengers, and they're looking for extremely rare contraband and extremely rare kinds of stuff that most of them probably never see, certainly in the course of a week, maybe in the course of their career.

So I think one of the things that we can do to help narrow down the list and improve effectiveness is to reduce the set of things that we have them looking for at the checkpoints. Liquids and some of the other kinds of contraband that they're looking for probably don't need to be on the list at this point.

JUDY WOODRUFF: Are you saying that because those don't pose the threat that it was thought they did?

JACK RILEY: Yes, I think there's growing consensus that the non-metallic liquid bomb issue probably wasn't as severe as people thought it was back in 2006 or 2007, when the restrictions first started being put in place.

There's never really been a credible demonstration of the ability to generate that kind of bomb outside of laboratory conditions. But one of the things that, it does is provides a tremendous distraction to TSA personnel as they look for liquids and other kinds of things at the checkpoints.

JUDY WOODRUFF: So what should they be focusing on?

JACK RILEY: I think that what they should be focusing on are the things that can be used to help bring down planes very effectively, and that really is a very small set of guns and bombs, the very kinds of things that unfortunately they missed in the testing.

JUDY WOODRUFF: Just quickly, Jack Riley, the other report that's come out indicates that, I guess out of — it was a large number of people, 900,000 active airport workers. They found 73 of them had unspecified links to terrorism. Should we — should people be concerned about that?

JACK RILEY: You know, I just had a chance to read that report before I came down for the interview.

It's a little tough to say. I would say that TSA has, through the airports and its own security force, a very large number of people that need to be cleared and have background checks on. What I'm looking for is their reaction to the I.G.'s report. And what I heard today was ownership of the lapses.

And I'm fairly confident that the new administrator of TSA is going to get on this very quickly, and I doubt we will be talking about it the next time there is this kind of investigation.

JUDY WOODRUFF: So, if one is to ask you, what's the main thing TSA needs to do differently going forward, what would you say?

JACK RILEY: I think the main thing is reducing the set of things that they're looking for, making sure that they have a focused mission, looking for the guns and bombs, and stepping back from some of the things like knives and other small objects that really don't pose a threat to bringing down the planes.

JUDY WOODRUFF: Jack Riley, vice president of the RAND Corporation, we thank you very much for talking with us.

JACK RILEY: Thank you.