John F. Harris is founding editor of POLITICO and author of "The Survivor: Bill Clinton in the White House."

So it looks like this might really be about to happen ...

A week ago, the idea of impeachment proceedings against President Donald Trump was something that the most hotly combative Democrats wanted but the most coolly calculating Democrats did not. House Speaker Nancy Pelosi, previously the lead voice of the skeptics, on Tuesday announced her about-face.


Pelosi's appraisal is partly about new facts relating to Trump’s dealings with Ukraine, partly about understanding the shifting politics of her own caucus, partly about her own gag-reflex and just how much of Trump’s defiance of Congress she can tolerate.

Pelosi, who had already been in Congress for 11 years at the time of Bill Clinton’s 1998 impeachment, well knows the nature of the process. For all the constitutional trappings, it is a political exercise, not a criminal one. Facts, and law, are important but secondary questions. Inevitably another question is primary: Which side are you on?

Fundamentally, Pelosi's calculations, and those of other Democratic leaders, are about a reading of history: an assessment that, when it comes to choosing up sides on the question of Trump’s fitness for office, the country right now is more like 1974 than 1998.

In the first instance, Democrats used the threat of inevitable impeachment to force a Republican president from office, reaping large political rewards for doing so. By the end of the Watergate scandal even GOP partisans were excoriating Richard Nixon’s abuses of power.

In the second instance, Republicans 21 years ago calculated that the solemn ritual of the impeachment process would create its own momentum to force Clinton from office, even though a clear majority of the public did not want this. As it happened, the primary sponsor of the Republican strategy, House Speaker Newt Gingrich, was soon forced out; a president who two years earlier did not break 50 percent in his reelection was easily acquitted in a Senate trial while enjoying approval ratings in the low 70s.

This is not 1974. The tribal instincts that drive which-side-are-you-on politics were in their nascent stages in the 1990s, and now shadow virtually every interaction of contemporary politics.

This speaker cannot possibly believe that a careful and judicious impeachment inquiry exposing wrongdoing by Trump is going to cause many House Republicans, or Senate Republicans if a successful impeachment leads to a trial, to say: Hate to say it, but the evidence here is pretty convincing.

It is at least conceivable that a parade of new evidence, or newly packaged evidence, could finally force self-protective Republicans in the midst of an election year to speak to this most transactional president in language he would not appreciate but would understand: Sorry, man, just business, but either you go on your own or we will push you. This was what happened in 1974, when in the end it was a delegation of Senate Republicans visiting the Oval Office that led Nixon to walk the plank.

More likely (at the moment, much more likely) is that a mostly party-line impeachment vote in the House would be followed by a party-line vote in the Senate, in which Republicans would have to carry their defense of what Democrats call indefensible into an election year.

By these lights, the allegation that Trump was using the presidency and the leverage of military aid to pressure Ukraine to investigate the activities of Joe Biden’s son represents such a clear abuse of office that GOP candidates will pay a terrible price for letting the Republican Party become indistinguishable from the pro-Trump party.

Even when Republican loyalists eventually abandoned Nixon, the party was drubbed a few months after his August resignation in the 1974 elections—sending a wave of young liberals to positions of power that in some cases they occupied for a generation. The backlash was strong enough to help lift Jimmy Carter over Gerald Ford in 1976.

But, as Pelosi well knows, the politics of which-side-are-you-on are not always predictable. Gingrich in 1998 calculated that once the public was confronted with the seamy details of Clinton’s affair with young White House aide Monica Lewinsky, and the lies he told to the public and in judicial testimony to conceal his behavior, a wave of public revulsion would swell. In support of this goal, he pushed for a full public release of prosecutor Kenneth Starr’s report on his investigation, filled with pornographic detail on cigars and Oval Office fellatio.

Revulsion did indeed swell, but it was against Gingrich and Republicans. Unwittingly, they had helped Clinton and his defense team frame the which-side-are-you-on question. The central issue was no longer whether people approved of a presidential affair or misleading people about it, but whether voters found Clinton or Gingrich the more appealing figure. Jay Leno joked that Clinton was doing so well in the polls “he is already planning his next sex scandal.”

It was precisely this fear of a backlash—that an attempt to oust Trump by a constitutional process might actually end up making him stronger, and enhance his chances for reelection in 2020—that was previously causing Pelosi and like-minded allies to go slow on impeachment.

The Trump scandals, of course, are different in kind than the Clinton scandals in critical ways. Most important, the allegations Pelosi is most intent in pursuing involve official duties, including allegedly mixing foreign policy with his own political interests. What’s more, Clinton’s standing with the public varied widely depending on the circumstances. Reflecting the tribal nature of his appeal, the ceiling and the floor on Trump’s support are rarely more than a few percentage points apart.

Even so, there is some continuity. The very foundation of Trump’s support, which carried him to power and has remained constant with supporters from such controversies as the “grab them by the pussy” tape in October 2016 to a parade of resignations and indictments of top aides ensnared in Robert Mueller’s investigation, revolves around his ability to prosper by posing the old, familiar question to his most loyal supporters: Which side are you on?