Julian Zelizer is a professor of history and public affairs at Princeton University, and author, with Kevin Kruse, of the new book " Fault Lines: A History of the United States Since 1974. " The opinions expressed in this commentary are his own. View more opinion at CNN.

(CNN) President Donald Trump has rightly come under intense criticism for his initial response to the horrific acts of terrorism that occurred at two mosques in New Zealand. After sending out a normal presidential message that offered his " warmest sympathy and best wishes " to the New Zealanders in the wake of the "horrible massacre," he then started tweeting about " Jexodus " (the alleged shift of Jewish voters to the GOP) and the Russia investigation. "THIS SHOULD NEVER HAPPEN TO A PRESIDENT AGAIN!" Trump wrote , conveying where his heart and soul are on this sad day. And when asked by a reporter on Friday if he sees an increase in white nationalism, Trump said : "I don't really, I think it's a small group of people that have very, very serious problems."

At this point, nobody should be surprised. In numerous times of tragedy, the President has been unable to offer the right words of sympathy. The usual sorrow and anger that we hear from the Oval Office are too many times absent from his lexicon.

Back in April 1995, another president offered a controversial response to a terrorist attack by white nationalists, but the debates about his words were less about a lack of empathy than his willingness to give a tough appraisal of the climate that fueled extremism.

President Bill Clinton's remarks came a few days after the tragic bombing on April 19, 1995, when Timothy McVeigh and Terry Nichols blew up a federal government building in Oklahoma City, killing 168 people. Initially, after the tragedy, Clinton offered the familiar kinds of messages Americans expect from their leader: condolences to those affected and assurance that the nation would get through the heartbreaking moment.

But then, days later, Clinton struck a very different tone . During an appearance before the American Association of Community Colleges in Minneapolis, Clinton pointed to the angry conservative airwaves and without naming names warned that, "We hear so many loud and angry voices in America today whose sole goal seems to be to try to keep some people as paranoid as possible and the rest of us all torn up and upset with each other. They spread hate. They leave the impression that, by their very words, that violence is acceptable." He continued: "When they talk of violence, we must stand against them. When they say things that are irresponsible, that may have egregious consequences, we must call them on it."

With this speech, Clinton was ostensibly connecting the world of conservative talk radio, which had vastly expanded since the elimination of the Fairness Doctrine in 1987 that required radio and TV stations to present both sides of a political issue, to the rapid growth of white militia groups in the 1990s and conservative politics. Although still in its infancy, the internet had also given rise to sites that served as gathering places for white extremists

Clinton's point was seemingly not to blame talk show hosts or right-wing Republicans for the bombing, but to offer a necessary warning that rhetoric can be dangerous. When hateful ideas are thrown out into the public square, they can inspire unstable individuals to do horrendous things or make organizations of hate feel empowered.

Predictably, conservatives responded angrily. Rush Limbaugh called the speech "irresponsible and vacuous " in suggesting there was any connection. Republican Sen. Don Nickles reprimanded the then-president by saying: "This incident wasn't caused by Rush Limbaugh; this incident wasn't caused by people who think government is too big." Some conservative hosts did become defensive, like G. Gordon Liddy who said that he didn't believe he was fueling the " lunatic fringe " when he told listeners he used drawings of Bill and Hillary Clinton as target practice.

Clinton refused to back down. "Words have consequences," he said after claims that he had used the Oklahoma City bombing to win political points, "To pretend that they do not is idle." He did, however, clarify that his warning was relevant to the left and right, wherever the "reckless speech" was coming from that had the capacity to "push fragile people over the edge beyond the bounds of civilized conduct and take this country into a dark place." In his memoirs, Clinton recalled that after the bombing he decided to do all he could "to change the atmosphere of bitterness and bigotry out of which this madness had come."

It turned out Clinton was on to something important, a situation that has only become worse over the decades. We have seen the toxic environment of our current times, where white nationalism is too close to the surface, manifesting itself in previously unthinkable ways. President Trump has been willing to traffic in dog whistles, suggestive retweets, conspiracy theories, and loaded rhetoric that has convinced figures like David Duke, the former Grand Wizard of the KKK, to support him.

Even worse, Trump is not alone. There is a universe of right-wing conservatism, from Iowa Congressman Steven King defending the term white nationalism , telling the New York Times, "White nationalist, white supremacist, Western civilization — how did that language become offensive?"

We have also witnessed the creation and legitimation of a media environment that has few editorial filters and a huge reach as a result of social media, that offers endless fuel to white extremist organizations and lone wolf terrorists.

White nationalist organizations within the United States often seem to draw on the same pool of rhetoric that we hear from mainstream politicians and pundits, as do the lone wolves. According to CNN , the man who sent pipe bombs to multiple targets last October had a van covered in paraphernalia, including a sticker reading "CNN Sucks," a chant that has been heard at Trump rallies . The manifesto of the New Zealand shooter offered words of praise for the President.

To be clear, the President, legislators like King and right-wing media pundits are not responsible for these horrific acts.

But we need to be equally clear that the incendiary rhetoric we constantly hear on our television screens and see on the updates of our computers and twitter feeds creates an incredibly dangerous environment.

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The danger of white internationalism, as we should be calling it, is growing. This is a major threat that all nations now face which has gained organizational clout and which has been impacting political parties. It is time for our leaders to not only show sympathy toward victims, but to launch an international coalition against this rising force of hate.