The spate of mail bombs sent to prominent Democrats this week has spurred news organizations to step up security measures, in another disturbing sign of the polarization that has created new dangers for journalists covering politics and divisive social issues.

The FBI and other law enforcement agencies have mounted a nationwide investigation into the source of the explosive devices addressed to such figures as former President Barack Obama, former Secretary of State Hillary Clinton and former Vice President Joe Biden. A package addressed to former CIA director John Brennan that was sent to CNN forced the evacuation of the Time Warner Center on Wednesday. Actor Robert De Niro was targeted early Thursday morning in a package addressed to him and sent to the office of his Tribeca Enterprises in New York.

The targeting of CNN and prominent critics of President Donald Trump has fueled speculation that the mail bomb spree is politically motivated.  President Trump’s relentless attacks on mainstream news organizations has spurred fears among journalists and others that activists and extremists will turn to violence. In June, five reporters were gunned down at the offices of the Capital Gazette newspaper in Annapolis, Md.

Related

New York Mayor: Suspected Mail Bombs Are 'Absolutely Terrorism'

Trump Intensifies Media Attacks as More Mail Bombs Are Discovered