Ten retired FBI officials and experts in counterintelligence sent a letter to Congressional leaders warning that the Biden administration's policies have facilitated a "soft invasion" of military-age men into the United States from terror-linked areas of the world.

The letter, written on Jan. 17, before Texas Gov. Greg Abbott invoked the invasion clause of the US Constitution, suggests that a terrorist attack is likely imminent.

"The threat we call out today is new and unfamiliar. In its modern history the U.S. has never suffered an invasion of the homeland, and, yet, one is unfolding now," the letter reads.