Threat letters with powder sent to McCain's offices

This is “breaking” news, so I might have to update this later. 

Two of John McCain’s campaign offices have received threatening letters containing white powder.  The offices in Denver and New Hampshire have been evacuated and HAZMAT teams have been sent in to test the substance.  There are no reports on any of the office workers falling ill as a result of the powder.

Related articles:
CNN – “Powder, threatening letter sent to McCain office”
FOX News – “Two McCain Offices Receive Envelopes with white powder, threat”
Reuters – “McCain Colo. office evacuated after letter threat”
Denver Post – “McCain’s Centennial HQ evacuated for white powder”
Washington Post – “McCain’s Denver Headquarters Evacuated”
First Door on the Left – “Powder at McCan offices”