Allies of President Donald Trump rejected any link between harsh political rhetoric and a rise in violence in the U.S., even as President Barack Obama's homeland security chief said changing the "toxic" political environment must start at the top.

The comments came after last week's attempted pipe bombings and the mass murder at a Pittsburgh synagogue on Saturday.

Deranged individuals infused with today's uncivil political discourse think it's their place to bring about change in society with assault weapons or bombs, and Americans listen to their leaders — including the president, said Jeh Johnson, the former secretary of homeland security.