The election of Donald Trump, and the early days of his presidency, have driven many Americans to rummage through history in search of context and understanding. Trump himself has been compared to historical figures ranging from Ronald Reagan to Henry Ford, and from Andrew Jackson to Benito Mussolini. His steps have been condemned as unprecedented by his critics, and praised as historic by his supporters.

To place contemporary events in perspective, we turned to a pair of historians of the United States. Julian Zelizer is a professor of history and public affairs at Princeton University. He is the author, most recently, of The Fierce Urgency of Now: Lyndon Johnson, Congress, and the Battle for the Great Society. Morton Keller is a professor emeritus of history at Brandeis University. He has written or edited more than 15 books, including Obama’s Time: A History. They’ll be exchanging views periodically on how to understand Trump, his presidency, and this moment in political time. —Yoni Appelbaum

Morton Keller: In his inimitable manner, President Trump has stirred up a mini clash with his predecessor, Barack Obama, by accusing him of having Trump's headquarters wiretapped during the 2016 election. Time, and investigation, should cast light on the substance of this charge. As historians, we can speak to the uniqueness of this sort of attack, and what light it casts on Trump's—and the current political culture's—way of doing business.

It is hardly unknown for a newly-elected leader to denigrate the performance of the previous incumbent. Think Franklin Delano Roosevelt and the hapless Herbert Hoover after the 1932 election, or Winston Churchill after he replaced Neville Chamberlain in 1940. But these were critical national moments—the Great Depression in America, the Nazi threat in Britain—and to underline the scale and significance of the change was deeply appropriate.

More germane to the current situation was Barack Obama's treatment of George W. Bush after the 2008 election. Bush's unpopularity, and the hope-and-change theme of Obama's campaign, dictated that he not let his predecessor off lightly. (Nor did his not modest self-estimation of what his presidency represented.)

But Obama's continued drumbeat of anti-Bush comments was downplayed by a sympathetic media, and in its own way, it reflected the national disapproval of how the Bush presidency had turned out.

Trump's onslaught differs in several important respects. For one thing, it is keyed more to the political needs of the present moment—to deflect attention from Russia's role in the election—than to the definition of Trump's presidency. It came out of the blue, related only tangentially to the Trump party line of being the populist victor in the face of an unprecedented barrage of hostility by the media, the Democratic opposition, and the privileged classes.

There is another distinctive characteristic of Trump's accusation: its lack of context, evidentiary or otherwise. In this sense it is not unlike the repeated claims of Hillary die-hards that Russian (or FBI) intervention explains her 2016 loss.

Trump's disconnected and thus far unsubstantiated wiretapping charge is most likely, I think, to wind up in the full-to-overflowing dustbin of his off-the-cuff tweets. But it may well be that helter-skelter skipping from one topic to another is the essence of the Trump style of governing (if one can dignify it with that word).

So I would expect, Julian, that over time this episode will sink into the Trumpian limbo of half-baked accusations with early sell-by dates. What do you think?

Julian Zelizer: It is healthy to remember that the essence of most presidential administrations, at least early on, is to define themselves against their predecessors. It is difficult to think of a president who didn’t spend a decent amount of time criticizing the person who came before him, particularly if that person was from a different party. Mickey, you are certainly correct in reminding us that Herbert Hoover offered a foil to Franklin Delano Roosevelt in 1932, and Jimmy Carter became a model of how not to do just about everything for Ronald Reagan. Richard Nixon basically blamed Lyndon B. Johnson for everything that had gone wrong for the U.S.—from Vietnam to urban unrest. Although he ended up keeping many of his policies intact, Barack Obama campaigned as the antithesis of George W. Bush and governed with ongoing signals about how he wanted to do things differently. It is true that there was no shortage of tough words about Bush’s record to come from Obama and his administration.

But this feels different. Foremost, this is not really about policy. Also, at this point, new presidents have usually shifted their focus away from the previous president toward their own agenda. Finally, Trump’s charges are about illegal activities. With the accusations about wiretapping, Trump made a pretty serious claim about his predecessor; even if it’s true that we should take these tweets with a grain of salt, that can’t really be ignored. In essence, Trump was saying, or at least implying, that the former president violated the law. He didn’t seem to have any hesitation about doing this, nor is anyone around him watching. He lacks the judicious demeanor of Obama and others. Even Nixon had a stronger sense of the need for caution in public.

At this point, we need to assume that he did this without any concrete evidence. While putting this into the “overflowing dustbin of his off-the-cuff tweets” might be the most tempting thing to do, the problem is that in this day and age many of his followers will believe what they have heard. This will play directly into the intense partisan eco-system that shapes our political culture and fuel the vilification of the other that makes for a difficult partisan divide. It also looks like congressional Republicans might launch an investigation.

The point is that the accusations are different from what we have seen in other presidencies, not simply in terms of substance or not only because of the lack of evidence, but because President Trump is doing this in a media environment that has changed substantially over the past 30 years. The increasingly partisan media, the speed through which information spreads nationally and internationally as a result of the internet, and the absence of strong filters in the production and dissemination of news means that these kinds of claims quickly and easily take hold in the public debate. With a president who is willing to tweet whatever is on his mind, no matter how spurious the claims might be, this can have dangerous effects on the electorate. It becomes increasingly difficult for many voters to separate fact from fiction.

I do think that the wiretapping tweet was different than those Democrats who have expressed concern about the many intelligence agencies who reported on the Russian intervention that took place in 2016 and asked how that impacted the election. While blaming the intervention as the sole cause of Hillary Clinton’s loss really ignores many of the factors that undercut her candidacy, it’s fair to question what role that intervention did play. With so many contacts between Trump and Russia officials, it is also fair at this point to ask questions about these connections.

The bad actions of presidents can have damaging consequences by lowering the bar as to what is considered respectable behavior. Many historians agree that many decades of excessive executive power and covert intelligence activities in the 1950s and 1960s culminated with the abuses that we saw with Richard Nixon. It feels like with this wiretapping accusation that Trump is really lowering the bar as to what is acceptable in national politics and what is out-of-bounds.

Keller: I'm in accord with much of what you say, though I do think you tend to judge the Democrats—Johnson, Carter, Clinton, Obama—by a more forgiving standard than you do the Republicans. After all, Obama's repeated accusations that Bush lied about nuclear weapons in Iraq, when any more likely explanation, surely, is intelligence failure, are easily up there with Trump's wiretapping probable-fantasy.

In terms of eventual consequences, wasn't Johnson's willful misrepresentation of the Gulf of Tonkin incident at least the equivalent of Watergate in the harm it did to America?

We can argue these matters ad infinitum, without reaching agreement. My own view is that there is not much to be gained by trying to come up with some moral cost accounting between Democrats and Republicans. I didn't like it when the GOP diehards and their media mouthpieces went on about Obama's unique perfidy, and I don't like it when the Democrats and their media mouthpieces adopt a similarly Manichean view of unblemished Democrats and irredeemable Republicans.

So I'd be inclined to leave Trump's wiretapping tale where it seems to be at the moment: an accusation so far without a definitive pedigree of proof or disproof, a not untypical Trumpian spinoff of the sort whose cumulative impact on our political life is distinctly harmful, but whose tone and character is, alas, all too common in our current political life.

Zelizer: If we are talking about presidential lying, a subject that Eric Alterman wrote a terrific book about, then certainly there are many Democrats who would come into focus, and you named some of the top contenders.

In terms of employing this kind of rhetoric, however, I am not as convinced as you are about both parties being on the same playing field, and this is something that we discussed in our last conversation as well. I am more persuaded by books like Asymmetric Politics and It’s Even Worse Than It Looks that the kind of partisanship that has taken hold in the modern GOP is much more extreme than among Democrats. Similarly, in terms of the kinds of attacks that President Trump has been willing to level against Obama, as well the kinds of lies he tells, it seems to me that Trump reflects something qualitatively different taking hold in the White House. Sometimes, “unprecedented” can be a crucial adjective to mark moments when our polity changes in some fundamental way. This is one of those times.