A White House whistleblower told lawmakers that more than two dozen denials for security clearances have been overturned during the Trump administration, calling Congress her "last hope" for addressing what she considers improper conduct that has left the nation's secrets exposed.

Tricia Newbold, a longtime White House security adviser, told the House Oversight and Reform Committee that she and her colleagues issued "dozens" of denials for security clearance applications that were later approved despite their concerns about blackmail, foreign influence or other red flags, according to panel documents released Monday.

Newbold, an 18-year veteran of the security clearance process who has served under both Republican and Democratic presidents, said she warned her superiors that clearances "were not always adjudicated in the best interest of national security" -- and was retaliated against for doing so.