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 ." Follow him on Twitter at @julianzelizer . The opinions expressed in this commentary are his own. View more opinion at CNN.

(CNN) On Saturday, the President of the United States retweeted a comedian's conspiratorial tweet, suggesting the Clintons may have been involved in the suicide of financier Jeffrey Epstein. That's right, President Donald Trump suggested that former President Bill Clinton was involved in murder.

It turns out Speaker Nancy Pelosi might have been onto something when she talked about Trump being "almost self-impeaching" several months ago. This August, Trump seems to be on a path of impeaching himself.

Despite the continued skepticism from Democratic leaders, the drive toward impeachment has accelerated. Over 50% of House Democrats, including some legislators from moderate swing districts, have announced their support for impeachment proceedings.

Even House Judiciary Committee Chairman Jerry Nadler, the emerging moral conscience of the party, said that he favors an impeachment inquiry, and contended that formal impeachment proceedings are already underway . He told CNN's Erin Burnett: "This is formal impeachment proceedings. We are investigating all the evidence, gathering the evidence. And we will (at the) conclusion of this -- hopefully by the end of the year -- vote to (send) articles of impeachment to the House floor. Or we won't. That's a decision that we'll have to make. But that's exactly the process we're in right now."

Nadler has done more than any other senior Democrat in talking about the "I" word and making the case to the public for moving forward with hearings -- the job of opposition leaders in these historic moments.

It is not clear that Robert Mueller's testimony before the House is the reason the impeachment process has accelerated. While the substance of Mueller's presentation was devastating, just like the written report, Trump himself has been the driving force in energizing Democrats to take a stand.

Trump has continued to do more than anyone else to maintain the political momentum necessary to prevent Democrats from putting the impeachment option aside. While the notion of self-impeachment is silly, it is true that Trump's own egregious actions forced Democrats to continue thinking about the kinds of dramatic steps that might be necessary to contain this runaway presidency.

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Trump's ongoing acceptance of white nationalist rhetoric, if not politics, continues to unsettle many across the country. It started with his tweet that said that the four young Democratic legislators who have been among his most vocal critics should "go back and help fix the totally broken and crime infested places from which they came," and continued with his racially saturated Twitter blast against Baltimore, and Maryland Rep. Elijah Cummings. And then there was the horrific shooting in El Paso where the crazed killer allegedly used the same word -- "invasion" -- as the President to describe immigrants in a manifesto before he prepared to murder innocent Mexicans in a Walmart.

The President's subsequent response in El Paso -- giving a thumbs up next to a baby orphaned in the shooting during a staged photo-op -- just made things worse.

In other words, the reason that impeachment is on the table has less to do with the Mueller report than the President's own actions. In the same way that President Andrew Johnson 's attacks on Reconstruction fueled the impeachment drive against him, the President's far right agenda is emboldening Democrats to consider voting for impeachment -- even if Senate Republicans will inevitably prevent his removal from office.

The worse that the President behaves, and the clearer the real world impact of his actions becomes, the easier it will be for Democrats to go on record saying that obstructing justice in a serious investigation is unacceptable. He tried, it would seem based on the Mueller report, to stifle the investigators in ways that President Richard Nixon would never have imagined possible.

We are still far away from that kind of vote. The fears that Pelosi has about a backlash to impeachment in moderate districts are very real and have not disappeared. Until she has the entire Democratic Caucus behind her, she will likely be reluctant to give her full support.

Trump, however, keeps making it difficult to just say no. His presidency is off the rails, and he is playing with a fire of racism, nativism and social division that is dangerous -- if not deadly. His rhetoric keeps getting more explosive as the election heats up. His retweet about the Clintons takes us into new "unprecedented" territory about just how far he will go.

Throughout his time in office, Trump has been his own worst enemy. Any other incumbent president with relative peace abroad, a good economy and a united party would be sitting pretty for reelection. However, he shows the nation every day the immense risks of giving him power. There is a reason his approval ratings have remained historically low and that he has never been able to crack majority support.

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Trump will only get worse, not better. Those who keep waiting for a "turning point" to normalcy are just not paying attention. The more heated that the 2020 campaign becomes, the more aggressive he will be. Every pillar of his rhetorical arsenal -- embracing nativism, demanding investigations and spreading conspiracy theories, dismissing law and order, and character assassination -- will remain front and center. With each swipe at this opponents, he will keep giving Democrats more fodder to take dramatic action to, at a minimum, go on record about why this kind of use of presidential power is not acceptable.