I've been tryin to think of an apt metaphor to help describe why I (and others - most notably, Dave Neiwert) believe that the extremist rhetoric which has become normalized as mainstream conservative rhetoric contributes to the breakdown of democratic discourse and increases the likelihood that such rhetoric will translate into acts of politically motivated violence.
I think I've settled on the metaphor of global warming and hurricane intensity. While we can not know with certainty that any particular hurricane intensity is the result of warming, we can expect that warming will tend to increase the intensity of hurricanes. Likewise, while any particular act of violence may not be linked with certainty to extremist rhetoric (also noting that an individual's behavior will have multiple interlinked causal factors) we can surmise that such rhetoric will increase the potential for politically motivated violence. I say surmise because unlike with global warming, this is not hard science, but conjecture; but if you've read Daniel Goldhagen's Hitler's Willing Executioners it's hard to escape the conclusion that it's well founded conjecture.
Which is why I'm willing to call the rhetoric of a member of Congress, who denies the citizenship of the first black American president (who happens to have a foreign sounding name) and labels him "un-American," calling him an "enemy of humanity" at the Christian nationalist "Take Back America" conferance, assasination fodder.
It was Obama's reversal of the "Mexico city" policy that urned the ire of Trent Franks, who accused the President of being dangerously godless and said that he should have "no place in any station of government." The rule reversed by Obama was one instituted by Ronald Reagan and George W. Bush, in which both presidents used the power of the Executive branch to impose their personal religious views on others by refusing to allow funding for international agencies which provide family planning services. See here for my previous commentary on the policy; and here where I note the irony of those who militantly seek to reduce the reproductive rights of women calling their oppenents "Nazis."
When we have a member of Congress speaking to an extremist Christian nationalist conferance that seeks to "Take Back America" from America's supposedly "first Muslim president," who is helping to bring about the New World Order, admonishing audience members to stock up on guns in preparation for "bloody battle" with Obama the Marxist Nazi, we have someone with the prestige of the United States Congress mainstreaming the sort of apocalyptic rhetoric that animates extremists to go out and kill.