President Trump has reacted to the House impeachment inquiry in predictable fashion, angrily denying any wrongdoing, spinning “witch hunt” conspiracies, and viciously attacking his accusers and political rivals, demanding, for example, that House Intelligence Committee Chairman Adam B. Schiff (D-Calif.) be “questioned at the highest level for Fraud & Treason.” On Sunday, he even embraced the suggestion that removing him from office could prompt a “Civil War like fracture.”

His combative response inevitably brings to mind President Andrew Johnson, another famous impeachment target whose contemporaries viewed him as emotionally volatile, publicly coarse and recklessly hostile to presidential and constitutional norms. Despite the many personal and stylistic similarities between the two, the political fallout of a Trump impeachment would be far more dangerous than any before.

The reason lies in how the powers of modern administrative government have become joined to partisanship in a polarized nation. This fusion has turned the contemporary party system into a weapon for the promotion of the president’s agenda and fostered a visceral base of supporters who disdain the virtues of deliberation, compromise and pragmatic government. While Congress must hold Trump accountable as an individual, we also must address these broader systemic flaws that have enabled him to undertake such behavior with impunity in the first place.

Like Trump, Johnson was vicious under political duress. At staged rallies, he compared himself to Jesus, launched into ruthless personal attacks against “traitorous” Republican opponents and called for the lynching of political rivals like Thaddeus Stevens and Wendell Phillips. Johnson’s extemporaneous harangues also included conspiracy theories accusing the “Radical Congress” of nurturing black violence in the South and “poisoning the minds of the American people” against him. The Republican press declared Johnson “a vile, drunken demagogue disgracing the presidency,” and even his allies lamented that “he is a slave to his passions and resentments.” Disgusted voters responded by giving anti-Johnson Republicans supermajorities in both houses of Congress.

That set up the titanic clash between Johnson and Radical Republicans in Congress that played out in 1868 and raised important constitutional questions. After Johnson dismissed Secretary of War Edwin Stanton in violation of the Tenure of Office Act, the House issued 11 separate articles of impeachment against him. Revealing just how dangerous Johnson’s harangues against his political enemies were deemed to be in the 19th century, one of the articles condemned the president’s inflammatory speeches for attempting to bring Congress into “disgrace, ridicule, hatred, contempt and reproach.”

Johnson’s Senate trial riveted the nation; newspapers covered each twist and turn with relish, and huge crowds packed the gallery (only after securing cherished admission tickets) to hear senators make their arguments. Johnson narrowly escaped conviction, but he was deeply isolated politically: A former Democrat who had joined Abraham Lincoln on the 1864 “national unity” ticket, he failed to unite a loose and fractious coalition of disgruntled Democrats, conservative Republicans and white Southerners. As a result, he failed to secure either party’s nomination in 1868 and limped off the political stage, a demagogue shorn of power.

And herein lies the difference between Johnson’s situation and Trump’s. Today, Trump is far from isolated or defanged. This is because two significant — and foreboding — developments have dramatically reshaped contemporary American politics: a deep partisan divide driven by movement activists, and an extraordinary concentration of unilateral administrative power in the hands of modern presidents.

On the left, activists pushed for civil rights, women’s rights and an antiwar agenda in the 1960s and 1970s, shifting power away from party bosses and elites. During the 1980s and 1990s, conservative evangelicals and other right-wing activists inspired by the Reagan Revolution transformed the GOP into a movement party with fervent commitment to traditional values and new election strategies that emphasized not reaching out to the mythical median voter, but mobilizing the party’s most fervent base supporters. In the years since, both liberal and conservative movement activists have pulled the parties away from the center, energizing grass-roots bases, shattering areas of postwar consensus and fueling ideological polarization and legislative stalemate.

In this context, political moderation and compromise win few, if any, rewards. Each party’s standard-bearers need not even evince the personal qualities valued by activists to win their devotion; the true test is whether they deliver the partisan political goods. As Liberty University President Jerry Falwell Jr. put it in explaining broad Christian-right support for Trump during the 2016 campaign: “We’re not electing a pastor-in-chief.”

And for Republicans, Trump has delivered the goods. While the mainstream press has focused on his incendiary tweets and scandals, the White House has undertaken base-pleasing initiatives, most of which did not require legislation, from the appointments of Supreme Court Justices Neil M. Gorsuch and Brett M. Kavanaugh to hard-line immigration positions, work requirements for Medicaid and rolling back some LGBTQ rights initiatives.

These executive actions, taken in support of what the Trump White House calls the president’s most “loyal customers,” explain why his approval rating has consistently had a high floor, regularly falling within a tight window between 39 percent and 44 percent. So long as this investment in the Trump administration remains strong, the president can inflict substantial harm on Republican lawmakers who break ranks, making any semblance of a bipartisan inquiry and resolution nearly impossible.

Trump also has allies in the media that Johnson never had. While Republicans controlled most newspapers in the post-Civil War era, by contrast, Trump’s direct appeals through Twitter are buttressed by the steadfast support of Fox News and most talk radio programs. With the assistance of media allies, Trump can exploit partisan divisions to produce public opinion on impeachment that mirrors intrinsic political fractures. The result is that impeachment raises the prospects of further tearing apart an already embattled nation.

Most accounts of partisan rancor emphasize congressional polarization, but the modern executive has also become more partisan as it has become more powerful. Since the days of Franklin Roosevelt, presidents of both parties have sought to achieve policy objectives by wielding administrative powers through the bureaucracy rather than navigating a complex system of separated powers to pass legislation. And so, as the fractious politics in Congress increasingly yielded gridlock, organized interests and movement activists have grown accustomed to executive orders that further their aims.

The Trump administration has embraced administrative aggrandizement from the start, and has vigorously used unilateral executive actions to serve its ends and those of its political base across a staggering array of policy areas. Such formidable power in the hands of a cornered yet unyielding political leader was something the architects of our Constitution never anticipated. As he has made clear, Trump will fight the impeachment battle by stoking support from his base. Already, the Trump reelection campaign is fundraising for a $10 million advertising blitz accusing former vice president Joe Biden and his son Hunter of corruption. The risk is that he employs the arms of government — the Justice and State Departments as well as the intelligence agencies — to further these accusations, while purging civil servants who balk.

Johnson, like Trump, was criticized for being crude, mendacious and unpresidential. But more profoundly, critics worried that Johnson was so intolerant and unrestrained that he threatened our most important constitutional and democratic norms. Supporters and opponents agreed on the need to constrain the actions of a dangerous demagogue and, more broadly, reduce the powers of the presidency, which had grown enormously during the Civil War. Because of his political isolation, Johnson ultimately inflicted less harm than he intended to.

Now imagine, however, if Johnson had had a fervent movement party behind him and the tools of modern presidency at his disposal. That is what we face today, spotlighting the challenges of fostering national resolve in the coming impeachment crisis. Restoring the health of our constitutional democracy requires us not only to hold an unprincipled president accountable, but also to address the fevered partisanship and vast executive powers that enabled him in the first place.