For more than a century, through world wars and technological revolutions, no American president faced removal from office for betraying the nation’s trust. On Wednesday, for the third time in many Americans’ lifetimes, a president will be pushed onto the very public path that could lead from commander in chief to defendant in chief.

The investigation launched after President Trump’s July 25 phone call from the Oval Office to the president of Ukraine will not only determine the fate of an unusually unpopular chief executive but also could have a decisive impact on the 2020 presidential campaign, the evolution of American power at a time of global political upheaval, and the social and economic gulf between Trump’s supporters and his critics at home.

This is the first impeachment process to unfold as a president seeks reelection and the first to take place in an era of instant and constant spin and ma­nipu­la­tion across social media.

The start of nationally televised hearings in the impeachment inquiry takes place in a deeply divided country, at a time of rapid and elementally dislocating change in the nature of work, the definition of community and the future of the planet.

Where the constitutionally vague and historically rare process ends, no one can know. Neither the congressional hearings and media reports that led to Richard M. Nixon’s resignation in 1974 nor the Senate trial that ended in Bill Clinton’s acquittal in 1998 could be accurately predicted from their starting points.

What is clear is that the nation begins this season of inspection seriously disunited — so lacking in basic mutual trust that impeachment seems to one side a cynical act of political aggression and to the other an unavoidable lunge to save the democratic system.

In much of the country’s conservative midsection, the impeachment initiative plays more as partisan ploy than as neutral search for truth, said Paul McNulty, president of Grove City College, a conservative Christian college outside Pittsburgh.

“People aren’t looking at this as a lot of Republicans looked at Richard Nixon in 1974, concluding that his behavior was something they couldn’t tolerate,” said McNulty, who served as deputy attorney general in the Justice Department under President George W. Bush. “They see it as a political act. I was involved in the [Bill] Clinton impeachment, and it’s the same thing all over again: People see this as something the Democrats have been meaning to do for a long time, just like Republicans were seen as having it in for Clinton in 1998.”

But for Americans who believe Trump poses a danger to the democratic system and the nation’s standing in the world, impeachment seems reasonable and even necessary.

“The president must be held accountable,” House Speaker Nancy Pelosi said in announcing the inquiry on Sept. 24. “No one is above the law.” Trump, she said, had betrayed “his oath of office, our foreign policy, our national security and the integrity of our elections.”

In a sharply divided country where relatively few people seem open to persuasion in either direction, it’s not yet certain that Americans will be riveted by the hearings. That’s a big change from 1973, when 71 percent of Americans told a Gallup poll they watched the Senate Watergate hearings live on TV, in many cases for hours at a stretch.

PBS aired gavel-to-gavel coverage of the hearings every day and repeated the broadcast each evening in prime time. Today, there are vastly more ways for people to see the hearings, on TV and online, but the explosion of entertainment options has made it harder for any single program to attract the kind of massive audiences that were achievable in a time when all Americans were focused on the same broadcast TV networks.

This time, many people will view the impeachment hearings through the prism of media outlets aligned with one or another ideology. Fox News and MSNBC were nascent enterprises when the Clinton impeachment unfolded in 1998; only about a quarter of U.S. households had Internet access at the time. Social media and its roiling underworld of conspiracy theories and extremist rabbit holes did not yet exist.

Even before a parade of witnesses testify about what the president did to try to get Ukraine to investigate former vice president Joe Biden, it’s clear that the impeachment story has elbowed the presidential campaign out of the spotlight that would otherwise have been shining on candidates vying to take on Trump.

In an analysis conducted for The Washington Post, the Tyndall Report, which monitors the big three network TV newscasts, found that since news broke about the Trump-Ukraine phone call, impeachment-related stories have dominated: Four years ago, the networks’ nightly newscasts, which still draw far larger audiences than the cable news channels, devoted 328 minutes to campaign coverage in the eight weeks before Nov. 6. This fall, during the same period, the newscasts gave the campaign only 59 minutes of attention, compared to 377 minutes on impeachment-related stories.

“The Ukraine story has deprived the campaigns of oxygen,” concluded the Report’s author, Andrew Tyndall.

Popular knowledge and opinion have been vital to the outcome of each impeachment process. Contrary to its judicial trappings, impeachment is more a political process than a judicial one. House members act as grand jurors, deciding whether to take a president to trial, senators sit as trial jurors, and the chief justice of the United States acts as the judge. But historically, senators have weighed the politics of the moment in their decisions at least as heavily as the evidence before them.

In the Nixon case — the first presidential impeachment drive since Andrew Johnson was acquitted in a Senate trial in 1868 — popular support for the president held strong until televised hearings began in the Senate’s investigation and didn’t completely collapse until tapes were released in the summer of 1974 showing the full extent of Nixon’s involvement in planning and covering up crimes. When that happened, Nixon’s removal from office seemed inevitable; the president, under intense pressure from fellow Republicans in Congress, quit.

Even before that, Republicans had joined Democrats in hearings that Frank Bowman, a historian of impeachment who teaches at the University of Missouri Law School, called “sober, lawyerly exercises — high public theater. The Republicans wanted to minimize what the president had done, but they didn’t denigrate the fact-finding mission, unlike today, when their performance has been consistently adversarial.”

In Clinton’s case, the president’s popular support only briefly dipped below 60 percent and actually grew substantially as the impeachment process moved along in the fall of 1998. The more the public learned about the case against the president, the stronger his support became, peaking that November with 71 percent of Americans saying he should not be impeached, according to a Post-ABC News poll.

“The Clinton impeachment was hideously and increasingly unpopular,” Bowman said. “It was pretty plainly a Republican suicide mission from the beginning. Any man with any sense of personal honor would have quit, but Clinton and his folks managed to change the public narrative from his bad behavior to the behavior of those who attacked him.”

After almost five months of hearings and a trial, the Senate voted not guilty by 55 to 45 on one count and 50 to 50 on another to acquit Clinton.

Trump seems drawn to the Clinton playbook, at least inasmuch as the president from the start has sought to focus attention on the motives and methods of those who are investigating him.

Trump’s efforts may be holding his base intact but don’t seem to be making any inroads on the rest of the country. Support for impeaching the president ranged from about 37 percent to 43 percent in various national polls before the Ukraine call came to light, but jumped to just under half by early October and has stayed close to that level ever since. In a Post-ABC poll in late October, 49 percent of Americans said Congress should remove Trump while 47 percent said it should not.

In a metric that didn’t exist the last time a president was threatened with impeachment, online prediction markets, where anyone can bet on the outcome of political events, are showing about even odds that Trump will be impeached this year. Participants are betting 18 cents on the dollar that the president will be convicted and removed from office, down from 23 cents three weeks ago.

Although Trump’s rebuttal to the case Democrats are mustering appears to be more improvised than, say, the war room that Clinton staffed with a battalion of top-shelf lawyers and spin doctors, it is nonetheless a response he has repeatedly practiced through a half-century of defenses against lawsuits, bankruptcies, business competitors and political critics.

He distracts, attacks, insults and declares himself a persecuted victim who fights back hard and never gives way, though in fact he often does.

“Life is about survival,” Trump once told one of his biographers, Michael D’Antonio. “It’s always about survival.”

Each embattled president has responded to impeachment in a distinctly different way, though in all three recent cases, the process began with rote denials and protestations about witch hunts.

Nixon stonewalled and contended he was “not a crook,” a baldfaced lie that collapsed when it was revealed that much of his “massive campaign of political espionage and sabotage,” as The Post’s Bob Woodward put it, had been caught on tape.

After initially stating that “I did not have sexual relations with that woman,” Clinton had to change course when independent counsel Kenneth Starr got proof from White House intern Monica Lewinsky’s blue dress and the president’s blood sample. “I misled people,” Clinton then said. “I have sinned.” But Clinton successfully argued that his misdeeds were, as then-House Minority Leader Pelosi said back then, “grounds for embarrassment, not for impeachment.”

Now, even as some of his Republican allies seek to carve out a middle path in which they acknowledge that Trump shouldn’t have mixed domestic politics into his dealings with a foreign leader but say the misdeed didn’t rise to an impeachable offense, the president insists there’s no need to concede anything. His conversation, he tweets repeatedly, was “perfect.”

Who will believe him? This will be the first impeachment process since the nation fell into a disorienting redefinition of trust. Both the Nixon and Clinton scandals were very much about trust; many historians trace the collapse of widespread trust in major American institutions to Watergate and Nixon’s betrayals. The titles on a shelf of books about Nixon tell the story: “Breach of Faith,” “The Imperial Presidency,” “One Man Against the World.”

By Clinton’s time, the nation’s ideological divide had opened. The Drudge Report had become a gossipy online tip sheet for Americans seeking a more populist news menu, and what Hillary Clinton would characterize as a “vast right-wing conspiracy” was amassing a huge audience on conservative talk radio and countless online chat rooms and blogs.

The Trump hearings begin as the very definition of trust is up for grabs. Americans report record levels of mistrust in institutions of government, religion, business and media, according to a Pew Research Center study.

Yet at the same time, the gig and sharing economies have transformed Americans into a people ready and willing to trust complete strangers to drive us around town, share our homes, borrow our cars and lend us money.

That confusion has carried over to politics and a recasting of how voters decide whom to trust as president: George W. Bush and Barack Obama both enjoyed stronger support for their character traits than for their stands on issues, according to the Gallup Poll, whereas Trump has flipped the script, winning more support for his actions in office than for his trustworthiness and honesty.

History teaches that impeachments reflect political reality more than judicial conclusions. America’s political reality in 2020 remains several turns of the calendar pages away.

Scott Clement contributed to this report.