Justice Department Inspector General Michael Horowitz said Thursday his office will launch an investigation into federal agents' "use of force" in Portland and the clearing of peaceful protestors in Lafayette Square in Washington, D.C., including the use of chemical agents.

Why it matters: Demonstrations in Portland against police use of force have continued in the city for more than 50 days. President Trump has threatened to send federal law enforcement into other cities run by Democrats.

The big picture: House Democrats asked the DOJ's Office of Inspector General to investigate the response of federal law enforcement personnel to ongoing protests in cities across the U.S.

What they're saying: "If circumstances warrant, OIG will consider including other issues that may arise during the course of review," Horowitz said in a letter sent Thursday to House Democratic leadership.

• "The review will include examining the training and instruction that was provided to the DOJ law enforcement personnel; compliance with applicable identification requirements, rules of engagement, and legal authorities; and adherence to DOJ policies regarding the use of less-lethal munitions, chemical agents, and other use of force."

Go deeper:Rand Paul denounces use of federal force in Portland