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On "The Kelly File" tonight, FBI counterterrorism expert Dr. Sebastian Gorka said that Americans should be on guard during the Thanksgiving holiday.

He explained that in the last 20 months, 82 individuals who were members of ISIS were killed or arrested on U.S. soil.

"The fact is ISIS is already here," Gorka said, noting that more than 4,000 Westerners have left their home countries to join ISIS.

"Those are people with Western passports - American passports, British passports. They will have freedom of movement," Gorka said. "That is the threat to America. It is real, it is actual."

He added that Americans should be on their guard particularly around the Thanksgiving holiday, since the essence of terrorism is to instill fear.

"They want to attack people who aren't ready in high concentrations and send a message of fear across the Western world and across the U.S. population," Gorka said. "As a result, you need to be on your guard. Americans need to be tactically aware, and they need to be observant of what's going on around them, especially now during Thanksgiving."

Watch more above.

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