The following press release was published by the U.S. Secret Service on Nov. 21, 2018. It is reproduced in full below.

Although the letters did not contain any hazardous materials, the U.S. Secret Service takes all threats and/or unusual direction of interest toward our protectees seriously. The matter is being investigating by the U.S. Secret Service and our law enforcement partners.

-- United States Secret Service

Source: U.S. Secret Service