BRUSSELS -- The attacks in Brussels exposed a gaping hole in the airport security net.

The Brussels airport bombs went off in the departure area -- before the security checkpoint. It's open to anyone, with or without a boarding pass.

At airports across country -- from the nation's capitol to California -- passengers were greeted by a heavily armed, stepped up police presence.

Officers checked arriving vehicles outside New York's JFK Airport.

In Miami, cart loads of customs officers patrolled the departure area.

But the attack in Brussels exposed a vulnerability at all airports -- the area before security checkpoints: the curb side, the ticket counter, even the line for coffee.

"The question is how do you best push those layers of security out -- recognizing there's no perfect system?" said former transportation security administration head John Pistole. "It becomes the question of do you bring in additional officers that you pay overtime to and how many bomb sniffing dogs do you have, and then once you start that how long do you sustain?"

Graphic shows the site of the blast inside the Belgium airport. CBS News

TSA said Tuesday it is increasing security at some airports, but it did not announce plans to push security perimeters back to cover softer targets.

Last March, a New Orleans man was shot by airport police while wielding a machete in the unsecured area of the city's airport.

In 2013, an armed man walked into LAX and killed a TSA officer outside the checkpoint.

"We're dealing with a large volume of people in confined spaces that are relatively easy targets," Ron Hosko a former assistant director of the FBI said. "We cannot secure every space, we cannot secure every space in America where people congregate, gather, we cannot do that effectively, and I believe our intelligence services and law enforcement working as hard as they are, are able to do it less and less effectively now because of the reality of encryption."

By encryption, Hosko is talking about secure phones and apps that let terrorists communicate undetected. There were calls in Congress Tuesday for strengthening airport security, but there will always be a soft target outside a security checkpoint.