The presence of unauthorized Iranian nationals on U.S. soil poses a national security risk of the highest level, former Obama Homeland Security Secretary Jeh Johnson warned - vindicating President Trump, who has consistently warned about the dangers of open borders.

"The presence in this country of undocumented migrants or Iranian nationals who have links to Hezbollah, IRGC, is, in my judgment, a domestic law enforcement concern of the highest magnitude," Johnson told Fox and Friends. 

Iranian immigration raises concern

The United States' involvement in Israel's war with Iran has led to heightened concerns about terrorism committed by foreigners, although no specific threats have materialized.

Trump immigration officials have arrested over 100 Iranians since Trump attacked Iran's nuclear facilities. Trump's strikes faced a largely symbolic response as Iran hit a U.S. base in Qatar with advance warning.

Although Trump has brokered a cease-fire between Israel and Iran, the federal government is vigilant about sleeper cells carrying out threats on U.S. soil, with the FBI reportedly shifting its focus to counter-terrorism efforts.

At least 700 known illegal aliens from Iran were released into the U.S. under Joe Biden, but the massive scale of the Biden-era border crisis makes it impossible to know just how many got across.

Some of the Iranians who have been arrested over the past week include an ex-sniper in Iran's military and a former member of the Revolutionary Guards (IRGC), an elite unit in Iran's military.

"That’s not necessarily all of them," Johnson said. "My educated speculation is that law enforcement has been tracking these individuals for a while in this country to follow leads, to see who they are in contact with." 

Trump vindicated

Adding to the concern is that "sleepers" do not need direct orders to pose a threat, Johnson noted, given widespread hostility towards the U.S. and Israel in the Middle East and Iran specifically.

"Sleepers don't necessarily follow the direction from their sponsors," he said. "Somebody who's here in the United States who has links to the IRGC, to Hezbollah, may decide to take matters into their own hands."

While the government has not confirmed any credible threats, the DHS is urging the public to be vigilant during a "heightened threat environment."

"‘If you see something, say something’ is still a valid public safety tool," Johnson said. "It does make a difference."

In the meantime, this national security concern is all the more reason to support Trump's crackdown on immigration.