(CNN) If impeachment of the president is always a match, today it is dropping into a much larger pool of gasoline than it did under President Richard Nixon or even President Bill Clinton.

After years of steadily rising partisan conflict, the inquiry that House Speaker Nancy Pelosi announced last week may be less likely to produce a consensus about President Donald Trump's behavior or fitness for office than an ominous awareness in both parties of how wide a trench in priorities and perceptions now separates red and blue America.

"It reinforces the divisions we already saw in 2016 and 2018 ... the mistrust, the dislike, the hatred among a good number of people toward the opposing side," says Alan Abramowitz, an Emory University political scientist who has extensively studied partisan polarization. "The negativity is going to get deeper."

Hardly any Republicans have objected to that bellicose rhetoric. If anything, Trump's conservative allies are matching him step for step in presenting the House inquiry as fundamentally undemocratic, if not un-American.

Former House Speaker Newt Gingrich, who was forced from office by his fellow Republicans over his handling of the 1998 impeachment effort against Clinton, declared this week that the House effort against Trump "is not an impeachment" and should instead be understood as "a legislative coup d'etat."

Looking at the gap that instantly opened between Democratic concern over Trump's actions and the refusal of more than a handful of elected Republicans to raise any questions, Democratic pollster Cornell Belcher is even more apprehensive than Abramowitz. Given "the outright collapse of time honored common sense political norms that once gave us at least a modicum of protection from cult like runaway partisanship," he tweeted last week , "u have to wonder if our Republic will ever recover."

Compared with 1974 or even 1998, the impeachment inquiry into Trump begins with the two political parties sorted much more distinctly along ideological, demographic, generational and geographic lines.

In Nixon's day

During Nixon's 1974 impeachment inquiry, which eventually led him to resign, the GOP still contained a significant number of moderate and even liberal officials representing constituencies in big cities and along the two coasts. Both the Democratic electoral coalition and the party's House and Senate caucuses, in turn, still relied heavily on support from deeply conservative Southerners.

That alignment produced complex legislative and electoral alliances that crossed party lines; Nixon, though remembered as a combative President, actually engineered a succession of bipartisan deals with congressional Democrats, especially on the environment. When Nixon took office for his second term shortly after his 49-state reelection in 1972, the Gallup Poll recorded that 51% of Democrats approved of his job performance.

Democratic voters and elected officials did grow steadily more comfortable demanding Nixon's removal as more information about the Watergate scandal emerged in 1973 and 1974, but in that less tribal environment, the confrontation never became a purely partisan standoff. When the House Judiciary Committee voted articles of impeachment against Nixon in July 1974, six of the committee's 17 Republicans joined all 21 Democrats in approving them . And after initially pledging to fight impeachment "to the end," Nixon resigned in August largely because leading Republicans, including former party presidential nominee Barry Goldwater, publicly warned him that most GOP senators would abandon him in a Senate trial.

In public opinion, too, impeachment did not entirely devolve into a partisan conflict. In the final Gallup Poll before Nixon left office, nearly one-fifth of Democrats still opposed removing him, while nearly one-third of Republicans supported it, according to detailed results provided by Gallup. That restrained the gap between the parties on whether Nixon should leave: In that survey, 31% of Republicans and 71% of Democrats thought he should go, a difference of 40 percentage points.

Clinton's impeachment

The parties had clearly grown more polarized by Clinton's time. But even so, in the years before his December 1998 impeachment by the House, the Republican-led Congress and Clinton had reached a flurry of bipartisan deals headlined by agreements to overhaul the welfare system and balance the federal budget. At least one-fourth of Republican voters in Gallup polling consistently said they approved of Clinton's job performance through his second term, and that number rose as high as about 40% as impeachment approached.

That didn't prevent a sharper partisan divide over impeachment in the House than under Nixon: On the first article of impeachment against Clinton that the House approved , just five Republicans voted no, while only five Democrats voted yes. But, again, the process stopped short of a complete partisan standoff. In the Senate, 10 Republicans voted against convicting Clinton on one House-approved article, while five voted against convicting him on the other. Clinton ultimately was not convicted by the Senate and remained in office. (All Senate Democrats opposed both articles, although some publicly criticized Clinton's behavior.)

And while 86% of the Democrats surveyed opposed removing Clinton in Gallup's final poll before the House vote that year, so did 26% of the Republicans, according to the results Gallup provided.

This time many signs indicate that the partisan chasm over impeachment, both in Congress and among the public, will be far deeper than in either of these two earlier cases. Compared with the Nixon and Clinton precedents, Trump's impeachment inquiry begins with the two parties already locked in much more intense conflict.

Today's landscape

Trump's presidency has featured hardly any of the bipartisan legislative agreements that built at least some goodwill under Nixon and Clinton. The two sides are still nursing wounds over the bruising Supreme Court confirmation last year of Brett Kavanaugh, who could face his own impeachment effort if Democrats win the White House next year. Trump has focused his policy agenda almost entirely on the preferences of his core supporters and has treated the parts of the country that resisted him more as a threat to mobilize his voters against than as potential supporters to be wooed.

Even before the inquiry began, Trump was in pitched legal and political combat with House Democrats over their efforts to conduct oversight of his administration. He enters this process with an unprecedented gap between the parties in perceptions of his presidency: In Gallup polling during the first half of September , just 5% of self-identified Democrats said they approved of his job performance, compared with 91% of Republicans.

The first major national poll conducted on the impeachment inquiry found a staggering partisan gap, far greater than under Nixon or Clinton: While 88% of Democrats supported opening an impeachment inquiry in the NPR/PBS NewsHour/Marist Poll conducted on September 25, just 6% of Republicans agreed. A two-day CBS survey released Sunday recorded a somewhat smaller division: While it also found that nearly 9 in 10 Democrats supported an inquiry, in its survey almost 1 in 4 Republicans did too. But that looks like an outlier: The national Quinnipiac University survey released Monday reproduced a wider division, with 95% of Democrats saying they supported an impeachment inquiry while 91% of Republicans opposed it.

A CNN Poll conducted by SSRS released Monday asked a sharper-edged question: Should Trump be impeached and removed from office? That survey found about three-fourths of Democrats already endorsing that prospect. It also recorded an increase since May among Republicans, though more modestly: Just 14% of them said Trump should be removed. (That was only about the same as the percentage of Democrats who backed Clinton's impeachment in Gallup polling just before the House vote in 1998.) Still, in a worrisome sign for the White House, the number backing removal rose to 22% among Republicans younger than 50.

Longtime Republican pollster Glen Bolger predicts that even if mainstream media outlets continue to reveal uncomfortable facts for Trump, his support among Republican rank-and-file voters is unlikely to significantly fracture so long as Fox News and the other leading conservative voices remain behind him. "What's happened is, and for good reason, conservatives and Republicans no longer trust the national news media to be fair arbiters or fair information purveyors," Bolger said. "So why would you expect anything different on this issue?"

And so long as GOP voters remain behind Trump, Bolger predicts, few elected Republicans will break from him. "It is going to be very unlikely," he says. "We are talking about two warring camps."

Battle lines are drawn

Stanley B. Greenberg, the veteran Democratic pollster and author of the recent book "RIP GOP," believes Trump could face more defections over time. While the President has virtually unshakeable loyalty from the evangelical Christians and tea party activists who compose more than two-thirds of the party, Greenberg says, his polls indicate Trump could face cracks among the remaining secular and more moderate GOP voters. He believes the Republican Party overall could face the same sort of internecine struggle already visible between some daytime and nighttime hosts at Fox News over the accusations. "The kind of fractures at Fox News will play out in the remaining party, perhaps even stronger," Greenberg said in an email.

All of those arguments will inevitably draw scrutiny and fact-checking from the media and rebuttal from Democrats. But the cumulative implication of those responses is larger than any specific assertion: It captures the extent to which elected Republicans are now operating in a political environment largely impervious to information in the mainstream media and that leaves them little room for independent judgment amid the demands for tribal loyalty. The modern GOP, notes Abramowitz, has become something of a closed circle: "It is very insulated from these external pressures that we would ordinarily see" creating incentives to break from lockstep defense of Trump.

And impeachment will compound each party's deepest suspicion of the other. Republican and conservative partisans will portray it, as Gingrich has already, as proof that the Democratic Party is so determined to transform America that it is willing to overturn the 2016 election. Democrats already see the Republican support for Trump as evidence that the modern GOP will accept almost anything from him so long as he offers the possibility of reaching 270 Electoral College votes -- and protecting the party's mostly white, Christian, non-urban voters from the implications of relentless demographic and cultural change that polls show many of them see as a threat to their role in society.

"They believe the barbarians are at the gate, and when the barbarians are breaking down the gate, nothing else matters," says Belcher. "That's the point where we are in our politics, and why Trump can get away with it."

Before it's over, the impeachment inquiry may force both sides to acknowledge that the capacity, and even interest, of red and blue America in reaching common understandings has eroded to a dangerous level. It may especially illuminate how much of the Republican coalition now rejects an underpinning of shared facts required to even pursue a dialogue with contrasting viewpoints -- as Jordan and McCarthy demonstrated in their bewildering television appearances last weekend.

Politicians in both parties, at their most uplifting moments, are fond of declaring that what unites Americans is much greater than what divides them. The blast-force pressure of the coming Trump impeachment battle will test that proposition even more than the battles over removing Nixon and Clinton from office.