Julian Zelizer is a history and public affairs professor at Princeton University and co-host of the "Politics & Polls" podcast. In January, Norton will publish a new book with Kevin Kruse, " Fault Lines: A History of the United States Since 1974 ." Follow him on Twitter: @julianzelizer. The opinions expressed in this commentary are those of the author. View more opinion articles on CNN.

(CNN) Americans suffered through a terrible week of hate that won't soon be forgotten. A psychologically disturbed supporter of President Donald Trump sent pipe bombs to a number of his top critics. Just days after the bombs began surfacing, a white man killed two African-Americans in a Kentucky grocery store after trying to enter a predominantly black church.

The week ended with the horrific massacre in Pittsburgh, when Robert Bowers walked into the Tree of Life Synagogue and opened fire, killing 11 people. He reportedly made anti-Semitic comments on social media before the attack, and to authorities after his arrest.

President Trump's visit to Pittsburgh in the wake of the synagogue shooting -- during which he placed stones on the 11 Star of David markers outside the synagogue, lit candles, and spent time in the hospital with patients who were injured in the attack -- won't do anything to allay the outrage of those who believe that the President has helped to aggravate our toxic national atmosphere, where white nationalists, anti-Semites, racists, nativists, and Islamophobes have come to believe that their ideas have somehow gained presidential legitimacy.

It is not a total surprise that some Jewish activists in Pittsburgh stated that they didn't want the President to visit the city until he fully denounced white nationalism while several government officials, including the Mayor of Pittsburgh , announced that they would not appear with the President in the grieving city.

The reason for this reaction is not just political, as his supporters keep arguing. It is a response to the much deeper questions about the administration's relationship to the forces of right-wing extremism.

There is now an ample body of evidence, from campaign ads to tweets, showing how then-candidate and now-President Trump has repeatedly used keywords and images that carry immense symbolic weight among white nationalist organizations and individuals.

From his campaign ad that some have noted featured anti-Semitic rhetoric , to his refusal to come down in straightforward fashion against neo-Nazis in Charlottesville, to his insistence on using the term "nationalist" despite the connotation it bears, it is not difficult to see why white nationalists would believe (rightly or wrongly) that he is on their side. His positions on key public policies, such as those regarding refugees and immigrants, play directly into the hands of extremists groups who support these ideas as well.

When President Trump wonders why former President Obama was not blamed for the shooting at an African-American church in Charleston, South Carolina, in 2015, he either misses the point completely or is not listening. After all, Obama was never accused, even by his harshest critics, of giving legitimacy to the ideas of white nationalists from the Oval Office. It was not a surprise, however, that the Anti-Defamation League has found a historic spike in anti-Semitism in 2017, Trump's first year in office.

Nor has President Trump done much to inspire confidence since Saturday morning's horrific shooting. After the President called the murders an act of evil and expressed his deep support for the families in Pittsburgh, he quickly returned to his standard way of doing business . During a rally on Saturday night in Illinois, Trump repeated his familiar talking points, railing against the news media, attacking Democrats and blasting Hillary Clinton.

Since then, things have only gotten worse. Indeed, President Trump and his spokespeople, including Sarah Huckabee Sanders, have decided that it is best to defend Trump's previous attacks on the media , while Vice President Pence made the odd decision to appear at a campaign rally in Michigan on Monday with a Messianic Rabbi, who believes Jesus was the Messiah.

Since the anti-Semitic hate crime, Trump and Fox News have only doubled down on their attacks on the immigration march that in their hyperbolic rhetoric is set on " invading " the country -- the same terms that Bowers used as he attacked the Hebrew Immigrant Aid Society, HIAS, before his deadly killing spree.

Tuesday began with a report of the President planning to sign a shocking executive order to revoke birthright citizenship , another example of "Trump playing with fire on the question of immigration to fire up his base," according to Jay Michaelson

If the President were serious about wanting to offer a response to white nationalism, he would be putting some realistic ideas on the table. Thus far, all he has talked about has been arming synagogues in America and supporting the death penalty for Bowers. As progressive Jewish leaders in Pittsburgh stated, Trump needs to start by offering a forceful, firm, and consistent denunciation of white nationalism, as a concept and as a movement.

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Trump should then follow through by moving to restore funding for community programs that actually help to stop the spread of hate groups. As Peter Beinart argued in a piece for The Atlantic , the administration has severely reduced funding for these efforts. And then, of course, there is gun control. If the President wants to be a true deal-maker, he should push his own party into some kind of grand compromise that includes regulations to stem the flow of assault weapons within the population. The students who witnessed the Parkland shooting are still waiting.

While it is good to see the President demonstrate some sympathy for those who were victimized in the sacred space of a synagogue, at this point a speech won't do much to convince those outside the base that he is serious about using his presidential power to actually tackle the hate and violence that shook America in October 2018.