The discovery of pipe bombs targeting prominent Democratic politicians and CNN is raising the threat of election-season violence largely unknown in the U.S. — and prompting uncomfortable questions about the consequences of leaders’ increasingly vitriolic rhetoric.

A sprawling investigation unfolded Wednesday as authorities scrambled to respond to a series of suspicious packages addressed to the homes of two former presidents, the offices of CNN and a former chair of the Democratic National Committee.

A bomb has been found at the home of Hillary and Bill Clinton in a New York City suburb, according to the Associated Press.