Editor’s Note: Julian Zelizer, a CNN political analyst, is a professor of history and public affairs at Princeton University and author of the book, “Burning Down the House: Newt Gingrich, the Fall of a Speaker, and the Rise of the New Republican Party.” Follow him on Twitter @julianzelizer. The views expressed in this commentary are his own. View more opinion at CNN.

CNN  — 

This is an historic day for the United States. President Donald J. Trump is now the first president in American history to be impeached twice – this time for his role in inciting an insurrection on the US Capitol, an abuse of power so egregious that somewhere former President Richard Nixon, disgraced over Watergate, is shaking his head in disbelief.

Wednesday’s vote should not be taken lightly. Only three US presidents have been impeached: Andrew Johnson, Bill Clinton and now Trump. But, as House Speaker Nancy Pelosi said at the start of the afternoon’s proceedings, “He must go. He is a clear and present danger to the nation that we all love.”

Although some Republicans will argue that both impeachments were driven by partisanship, in neither instance were Democrats particularly excited about having to spend their time rebuking a sitting president. In 2019, Pelosi had resisted pursuing the first impeachment process, fearing that voting to punish Trump would only embolden his supporters and improve his chances for reelection in 2020. She and many other Democrats further worried that impeaching over findings in Special Counsel Robert Mueller’s investigation of Russia’s meddling in our election or other potential abuses of power would ultimately hurt the party’s standing politically – even if it was the right thing to do.

Yet, when the details emerged of Trump’s call to the Ukrainian president asking for political dirt on his rival Joe Biden, Pelosi made a difficult decision to pursue charges. She did so knowing that there was little chance of conviction in the Republican-controlled Senate and that the GOP would politicize it for months to come.

The second impeachment was not politically convenient either. The vote came at a time when the party would much rather be focused on preparing to help President-elect Joe Biden enact his ambitious economic agenda during his first months in office. Taking on impeachment in the final days of a one-term presidency is just about the last thing that Pelosi or likely any Democrat had in mind as a top priority.

Nonetheless, once again believing it was the only right thing to do, they moved forward.

Impeachment serves many purposes. Most important, this constitutional process provides a mechanism for Congress to remove a sitting president who has abused his power and poses a danger to the republic he leads.

Trump’s abuse of power, which placed and continues to place every member of Congress in grave danger – as we saw, horrifyingly, last week – is simply unacceptable.

But impeachment is also a way for Congress to make a firm statement on the historical record about the limits of presidential power. The outrage that drove Wednesday’s vote did not come from partisan anger, at least not exclusively. It came from the feeling that the President’s role in the violent attack on the Capitol was a flagrant abuse of his authority – and one for which he continues to deny any responsibility.

Sadly, even as House members voted, an ongoing threat of further violence loomed. Military and security personnel are stationed in and around Capitol Hill to protect members of Congress from potential future attacks. Meanwhile, FBI reports indicate that more violent protests are being planned at all 50 state capitals and Washington DC.

Wednesday’s vote for impeachment creates a precedent for future elected officials when another politician tries to trample constitutional norms and undermine democracy. But, perhaps, most significantly, it marks a turning point: Now we, as a nation, can start to heal from the nightmare that was the Trump presidency.

As for the 197 Republicans who voted against impeachment, they will forever have to defend their records. The GOP can talk about the problems with a rushed impeachment process, but in the end their vote represents an acceptance of the erratic and dangerous behavior the President has engaged in since the November election.

If party members want to talk about separating themselves from Trumpism, this vote confirms that they have done just the opposite. Trumpism is Republicanism – pure and simple. As the presidential train veered off the rails, most Republicans sat right next to Trump and, whether in action or in silence, encouraged him to speed along.

Each impeachment is remembered in different ways. The impeachment of Andrew Johnson generates conversations about the collapse of Reconstruction and the subversion of efforts to achieve racial justice after the Civil War. The near impeachment of Nixon (who resigned instead) has stimulated dialogue about how presidents can dangerously misuse their authority in pursuit of self-interest. And the impeachment of Bill Clinton has become a basis for conversations about the weaponization of the process.

Trump’s dual impeachments will likely go down as an acknowledgement of the immense dangers that our republic has found itself in after the radicalization of the Republican Party resulted in a near total abandonment of norms and institutional restraints. When partisanship triumphed over the needs of governance and the health of our democratic institutions, violence ensued. Trump was a president who was willing to say and do almost anything in pursuit of power – and a majority of the GOP supported him every step of the way.

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    Although the President will likely complete his final days in office – as a Senate trial date has yet to be set and it remains unclear if enough Senate Republicans would vote to convict him – the action by the House won’t be forgotten. Under the direction of Pelosi, a bipartisan majority delineated a much-needed marker for what is not permissible in presidential politics and why certain actions will not be tolerated.

    The problem is that this won’t be enough. The impeachment is an historic step in the effort to improve the political health of the nation, but it can’t be the last one. The process of strengthening and restoring the system of checks and balances must be a top priority in coming years. Congress must tackle the broken structures and broken norms that allowed Trump to do what he did. Otherwise, we are bound to find ourselves right back where this started just one week ago.