David Greenberg, a professor of history and journalism and media studies at Rutgers, is a contributing editor at Politico Magazine. He is the author of several works of political history including, most recently, Republic of Spin: An Inside History of the American Presidency.

The internet is awash in historical explainers and hot takes trying to make sense of our sudden constitutional crisis. Marshalled on behalf of a range of competing viewpoints, the arguments are sprinkled with references to Andrew Johnson, Richard Nixon and Bill Clinton—the three presidents who faced impeachment proceedings before Donald Trump. Which one applies to the current president and his apparent effort to enlist Ukraine in going after Joe Biden, his potential opponent in the 2020 election?

Turning to the past is understandable: A presidential impeachment cries out for historical context. The past is supposed to offer a map of sorts through what feels like an unfamiliar and treacherous adventure. But—as historians, ironically, are sometimes the first ones to point out—history isn’t actually a very good guide here. We’re in uncharted waters, and it’s best that we recognize that.


Why do the Johnson, Nixon and Clinton examples offer us so little direct help today? Every impeachment poses two discrete sets of questions for the House and Senate to consider. First, there are constitutional questions: Are impeachment and conviction justified? Second, there are political questions: Are impeachment and conviction possible? With every previous presidential impeachment, the answers have been different, and in the case of Trump and Ukraine, the answers are different still. We’ve simply never had a case before where the removal of a president was so well justified—while at the same time so obviously unlikely to happen.

The 1868 impeachment of Johnson grew out of a power struggle between a reactionary president and the “Radical Republicans” who held power in Congress. Having assumed the White House after Abraham Lincoln’s assassination, Johnson—a Southerner who never left the union—warred with Republicans over a series of bills dealing with civil rights for the newly freed slaves and the terms for readmitting secessionist states.

The conflict crested when the Republicans passed the Tenure of Office Act, a law of uncertain constitutionality that barred the president from firing a member of his Cabinet unless the Senate approved a successor. Annoyed by Congress’ efforts to tie his hands, Johnson fired Secretary of War Edwin Stanton, a Lincoln administration holdover, without securing Senate approval—creating a test case of the new legislation. Johnson’s defiance provoked the House to swiftly pass 11 articles of impeachment, most of which dealt with the Tenure of Office Act.

Johnson was duly impeached. But he ultimately dodged removal from office because moderate Republicans came to his aid in his Senate trial. With no vice president in place, his ouster would have awarded the presidency to Senate President Pro Tempore Benjamin Wade—a fiery radical unloved by the moderates. Johnson sent word that he would relent in his fights with the Republicans if they let him stay in office, helping him to prevail by just one vote.

In Johnson’s case, the constitutional questions—are impeachment and conviction justified?—were open to debate. Generally, historians today tend to think his impeachment wasn’t warranted (even if they mostly agree that the Republicans were correct on Reconstruction policy). As for the political questions—are impeachment and conviction possible?—the narrowness of Johnson’s acquittal makes clear that the undertaking was hardly doomed to futility. It was a meaningful exercise that could well have gone differently.

A century later, the case of Nixon and Watergate furnished a different set of answers. The House Judiciary Committee didn’t pass its articles of impeachment against Nixon until July 1974, a full two years (and one reelection campaign) after the failed burglary and bugging operation that began the unraveling of Nixon’s vast dirty tricks machine. In those two intervening years, a Senate investigative committee—along with the criminal trials of the apprehended burglars, and reporting by dogged journalists—pried loose an avalanche of evidence about abuses of power and obstruction of justice in the White House that slowly but steadily shifted public opinion. Those counts, as well as one for Nixon’s defiance of congressional subpoenas, were powerful enough to convince several Republicans to join the Democrats in supporting Nixon’s ouster.

In Nixon’s case, then, impeachment charges were clearly justified on constitutional grounds. And as Nixon discovered in August, when the Republicans’ elder statesman, Barry Goldwater, led a delegation to the White House to tell the president he had lost almost all his fellow Republicans’ support, conviction was not just possible but virtually assured. Politically, too, impeachment was a slam-dunk. Capitulating to reality, Nixon resigned before he could be impeached.

Clinton’s impeachment a quarter-century later, for allegedly lying about his affair with White House intern Monica Lewinsky, yielded still a different combination of answers. The probe of the president’s sex life by Independent Counsel Kenneth Starr was something of a rogue operation to begin with, since Starr had been appointed to look into a wholly discrete matter—a real estate investment Clinton had made while governor of Arkansas (on which Starr could come up with no case for impeachment). From the start, Starr’s inquiry lacked a fundamental legitimacy, and while many Washington pundits nonetheless cheered it on, majorities of the electorate saw it as a partisan, not a constitutional, undertaking.

Was Clinton’s removal from office ever a real possibility? Probably not. It is true that when news of his dalliance broke, some people thought his days were numbered. But within a matter of weeks, public opinion turned decisively against Starr and toward Clinton, where it would remain. After taking up impeachment in October, the House Republicans promptly lost congressional seats in the 1998 midterm elections—an almost unheard-of development—providing strong clues that their partisan crusade would founder in the Senate, where even some Republicans came to voice qualified support for the president. When Clinton finally won acquittal in February 1999, it seemed like a long-delayed foregone conclusion. The outcome drove home the recklessness of pursuing an impeachment that was bound to fail.

So, what precedent do these impeachment cases provide? Johnson’s removal from office was possible but probably not justified (and thus ill-advised). Nixon’s was both possible and justified (and thus effective). And Clinton’s was neither possible nor justified (and thus farcical). Removing Trump from office over the Ukraine scandal would be different from all of these cases. Unlike in Clinton’s case, the constitutional argument for it looks increasingly powerful: We have fairly damning evidence from the White House itself of a direct conversation between Trump and the Ukrainian president about going after Biden. But unlike in Johnson’s and Nixon’s situations, removal is all but guaranteed never to happen—owing to the Republicans’ strong majority in the Senate and a disciplined tribalism of a ferocity that simply didn’t exist in the Nixon era.

Until now, many Democrats seemed to be reading the present through the past—in particular through the lens of the Republicans’ self-defeating anti-Clinton crusade. Their reading of history suggested that, given the sheer unlikelihood of actually dispatching Trump from the White House, it would be folly to press ahead with impeachment. That strategy seemed like a recipe for a bloody political fight, and even greater voter cynicism than we have now.

Only this past week did Democratic opinion dramatically shift. One reason seems to be an unwillingness to make the same mistake twice. Back in October 2016, evidence was mounting that Russia was meddling in the ongoing presidential election, along with suspicion that Trump’s campaign was encouraging or welcoming the interference. While Hillary Clinton spoke out bluntly, the administration at the time dithered, with President Barack Obama warning Vladimir Putin to “cut it out.” Everyone assumed Trump would lose the election and saw no reason to raise needless alarms. But the Ukraine scandal starkly evokes 2016—Trump seemed to have encouraged a foreign power to interfere on his behalf in an election—and Democrats grasped that they couldn’t run the same script as last time.

Still, to say the Democrats felt it necessary to finally begin impeachment proceedings isn’t to say the political risks are gone. Without any prospect of winning Republican supporters for Trump’s ouster, the Democrats’ ultimate objectives are troublingly unclear. Impeachment could galvanize voters against the president, but it could also backfire, as Bill Clinton’s impeachment did against Republicans. Or, like so much else in our polarized environment, it could just fail to move the needle.

No impeachment case in U.S. history yet has offered a perfect precedent. In fact, each one has reshaped our thinking about impeachment in the years afterward. The ill-advised impeachment of Johnson played a part in discouraging Congress from trying it again for more than 100 years. The successful revival of the impeachment machinery to use against Nixon, conversely, emboldened Republicans to try it against Clinton. And the abuse of the process against Clinton until now had deterred Democrats from using it against Trump. Whether the proceedings against Trump will open the floodgates to ever-more promiscuous uses of impeachment or serve to restrict its use only to the gravest of circumstances is unknowable. But one way or another, it is likely to redefine our politics for years to come.