Editor’s Note: Julian Zelizer is a history and public affairs professor at Princeton University, editor of “The Presidency of Barack Obama: A First Historical Assessment” and co-host of the “Politics & Polls” podcast. Follow him on Twitter: @julianzelizer. The opinions expressed in this commentary are his own.

CNN  — 

A few weeks ago, several political officials, and numerous journalists, jumped down the throat of comedian Michelle Wolf for making pointed remarks about the Trump administration at the White House Correspondents Dinner. The jokes, the critics said, were too harsh and further eroded “civility” in Washington. Ari Fleischer, former press secretary to President George W. Bush, said that Wolf’s jokes about Sanders were “uncalled for. It’s nasty.”

The past 24 hours have made it clear that Wolf really wasn’t the problem. With some jarring events in recent days the nation got another taste of the kind of bitter rhetoric that has become normalized during Donald Trump’s presidency, even between members of the same party.

On the heels of reports that Sen. John McCain, who is struggling against cancer, doesn’t want the President to attend his funeral, and after news broke that the senator opposed the administration’s pick for CIA director, White House aide Kelly Sadler joked to colleagues in an internal White House meeting: “he’s dying anyway.” There was no political commentary that was the basis of Sadler’s remark and it sounded malicious.

President Trump and Sen. McCain have always had a tense relationship. During the 2016 campaign, Trump criticized McCain for having been captured during the Vietnam War. “I like people that weren’t captured,” Trump said. Indeed, this kind of rhetoric may well have been the reason that the senator seemed to take particular delight in making a late-hours appearance for the vote last July on the administration’s failed legislation to repeal Obamacare … and to give it a dramatic (and literal) thumbs down.

And the race to the bottom has accelerated quickly. In another unseemly – jaw-dropping, even – slam at McCain over his opposition to torture, on Thursday a military commentator on Fox Business Network, retired Air Force Lt. Gen. Thomas McInerney, said: “The fact is, is John McCain – it worked on John. That’s why they call him ‘Songbird John.’”

Certainly, the coarsening of our political discourse cannot be pinned on Donald Trump. For over three decades, the nation has watched as politicians have lowered and lowered the bar for what they are willing to say publicly about each other.

Few members of Congress were totally prepared for the moment when South Carolina Republican Joe Wilson shouted out “You Lie!” to President Barack Obama as he spoke to a joint session of Congress about his health care proposals in 2009. The vicious language that has been used as Democrats and Republicans have moved farther apart is well-cataloged; the airwaves and the internet are filled with endless examples of political opponents demonizing and dehumanizing each other.

It is President Trump who has given this kind of rhetoric his imprimatur – in fact, in many instances demonstrating himself just how it’s done.

Every presidency helps establish the standards and norms under which we conduct our democracy. While all presidents in recent decades have been willing to jump into the tough partisan fray, Trump has been exceptional in the kind of language that he has regularly used on opponents – and in public. This is one of those cases when it is fair to use the term “unprecedented.”

Unlike his predecessors, he never made any shift away from the fierce broadsides that he delivered on the campaign trail, and in many cases he has doubled down on the kinds of “unconventional” – often personal – attacks about politicians and policymakers (as well as reporters, celebrities and activists) who stood in his way. When it comes to throwing insults, President Trump has no equal.

He has helped to cement an unfortunate new normal– a cultural change – in Washington, which explains why an official such as Sadler might not think twice about these kinds of remarks. This is, after all, the political world we now live in.

Without a top political leader trying to push back on these trends – as Presidents George W. Bush and Barack Obama both insisted on doing – there is no role model to remind us of our better political angels. Future presidents will feel that they can “go there,” if they want, without political repercussion.

While it is true that rhetoric is only a small part of the story in our democracy (policy and politics have the greatest sway) the way in which we talk about each other plays a part in setting the tone for our democratic process. The Sadler joke was much worse than anything Michelle Wolf ever said because it was done by a White House official in an official meeting and underneath a President who has repeatedly made even more objectionable statements.

After the story blew up in news reports, Sadler called Meghan McCain, the senator’s daughter, to apologize, a source close to the situation told CNN.

Sometimes a joke is just a joke, and we should appreciate the value of tough humor. But in other cases insults and barbed language reflect deeper dysfunctions in our political system. And if this does not concern you, it should.