Police with machine guns at U.S. airports this holiday weekend

WASHINGTON -- Security at home will be tighter as millions of Americans head out for the holiday.

Are copycat terror attacks possible in the U.S.?

Police at Los Angeles International Airport today are armed with automatic weapons. This Thanksgiving week -- amid ISIS threats -- there will be a larger police presence than usual in New York.

"I think it quite clear what we're advocating, seriously, is don't be afraid, be aware. It is part of the new world we live in," said New York City Police Commissioner Bill Bratton.

A new intelligence bulletin sent to law enforcement around the country warns there could be copy cats looking to replicate the Paris attacks in the U.S.

Former Assistant Director of the FBI, Ron Hosko said of the ISIS strategy, "a large proportion is about fear. Could something happen? Yes. But is there a greater chance of being struck by lightning? Or struck by a car on the way to D.C.? Yes."

Ex-CIA insider on overseas travel alert, policy against ISIS

Today, President Obama tried to reassure the public when he made a statement. "What happened in Paris is truly horrific. I understand that people worry that something similar could happen here. I want you to know that we will continue to do everything in our power to defend our nation," he said.

The strategy to protect the U.S. from terrorists involves studying tactics used in Paris.

Intelligence officials believe the attackers conducted pre-operation surveillance. Police in the U.S. are being advised to be on the lookout for suspicious people conducting surveillance of soft targets.