Update: No injuries have been reported, but a dozen people were exposed to the unidentified substance. Several have taken themselves to the hospital as a precaution. Hazmat crews are on the scene, federal authorities have been notified, and Postal Inspector agents are investigating. Developing…

Update: Both his Denver, CO and Manchester, NH offices have received the letters and have been evacuated.

Update: Drudge calls it a “death threat”.

Across on Fox. Not many details yet, but an envelope with white powder and a threatening note arrived at Mav’s Denver office.