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.

JUST WATCHED Sanders confirms Kelly Sadler still has a job Replay More Videos ... MUST WATCH Sanders confirms Kelly Sadler still has a job 01:31

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.

Read More