Arrest over letter to Trump containing poison ricin

The big picture: The FBI and Secret Service are investigating after two tests confirmed the presence of the toxin following the interception of the mail earlier this week, CNN first reported.

• All mail addressed to the White House is sorted and screened at an offsite facility before reaching the White House.
• The Royal Canadian Mounted Police said in a statement it was assisting in the investigation after receiving a "request for assistance from the FBI in connection with a suspicious letter sent to the White House."

What else they're saying: "The FBI and our U.S. Secret Service and U.S. Postal Inspection Service partners are investigating a suspicious letter received at a U.S. government mail facility. At this time, there is no known threat to public safety," the FBI said in an earlier statement.