It was this time last year that two ISIS supporters killed 14 people at a holiday party in San Bernardino, California. In light of theBerlin Christmas market attack, CBS News is following security here at home.

Heavily armed units patrolled Christmas markets in New York and Chicago Tuesday.

In Atlanta, police said “they are monitoring the situation,” while Seattle police announced a “heightened level of awareness.”

Monday’s attack comes six months after a man drove a truck into a crowd in Nice, France, killing more than 80 people. Just last month, a student at Ohio State University drove a car over a curb and then stabbed bystanders with a knife.

On “CBS This Morning,” deputy commissioner John Miller said the NYPD is working with the trucking industry to prevent vehicle attacks.

“One of the second things we did after the Nice attack was to go back out to 140 truck rental locations and say here’s some indicators of suspicious behavior,” he said.

According to a Congressional report, 80 percent of the terrorism cases being investigated by the FBI are related to ISIS. The group’s propaganda asks sympathizers to use vehicles to target outdoor markets, festivals or parades.

In response, cities like Cleveland have installed concrete barricades and fencing during special events. But Ron Hosko -- a former assistant director of the FBI -- said even that may not be enough.

“This low-intensity style attack that can be effectuated, committed by a baseball bat, by a knife, by a handgun, by a vehicle, that the opportunity to commit that style of attack is everywhere,” he said.

Police officials said there is no credible or specific threat. But, one of the things that continues to frustrate police is how quickly someone can go from “inspired” to action.