Federal probe of letters with unknown substances widens to Republican senators Collins, Cruz, Ricketts and Rounds

Earlier targets were Democrats and election offices.

Earlier letters went to at least 26 state election offices and at least 22 offices of congressional Democrats, per NBC News; Pete Ricketts (Sen-R Nebraska) said tests showed the powder sent to his Omaha office was not harmful.

Who got mail:

15+ House members said their offices received mailings Friday, Oct. 16 (The Hill).
Mike Rounds (Sen-R South Dakota), Ricketts and Ted Cruz reported letters at their state offices.