WASHINGTON — Next, more of the same, but with more entrenched division, a bitter crossfire of allegations and then, finally, a reckoning in the form of the 2020 presidential election.

The long-awaited conclusion of special counsel Robert S. Mueller III's investigation into Russian interference in the 2016 election is likely to harden congressional Republicans' wall of support for President Trump, strengthen Democratic demands to hold Trump to account — and result in little change in public opinion, according to historians and politicians who have studied past national scandals.

Mueller's conclusion — he found no evidence of collusion with Russia but was unwilling to exonerate on obstruction of justice — is likely to propel Washington into a period of prolonged and even more heightened partisan combat. The report, as summarized Sunday by Attorney General William P. Barr, contains fuel enough for both sides to cling to their version of the truth about the Trump campaign's ties to Russia, and not nearly enough for either side to alter their views.

"It may well be that a good portion of the Republican base will continue to see this as a witch hunt," said David Greenberg, a historian of the presidency at Rutgers University. "In the past, in Watergate and in Iran-contra, some Republicans have been willing to break with their president, but now we're just in a different cultural moment in terms of partisan and ideological rigidity and a right-wing media that keeps the party united behind Trump."

The report is going to deepen the pain and the antagonism.

Trump's supporters in Congress and around the country are likely to tighten their embrace of the president in light of Mueller's conclusion that he did not find evidence that Trump campaign staffers conspired with Russia to influence the 2016 election. The news already allowed many Republicans an exhalation of relief on Sunday, fueling hope that some Trump skeptics might be won over and postponing what many conservatives say is an inevitable redefinition of what it means to be a Republican.

"There's no middle on this' divide on Trump, said Craig Shirley, a biographer of the late president Ronald Reagan and a former Republican political consultant. "The report is going to deepen the pain and the antagonism. Even in the first 48 hours after the report was filed, when nobody knew anything, we saw both sides creating their own narrative and conclusions. For now, the party will continue to stand by Trump because of loyalty, fear and political reality."

Democrats, meanwhile, are likely to view Mueller's decision to lay out the facts about any possible obstruction "without reaching any legal conclusions," as Barr put it, as an invitation to further investigation — just as past presidential scandals have led to congressional hearings.

Although many Democrats on Sunday renewed their commitment to a wide-ranging investigation of Trump, Mueller's findings may have complicated their work ahead. Instead of simply reiterating a prosecutor's findings of fact, Democrats in Congress now face the task of pushing back against or at least expanding upon an investigation that they spent the past couple of years defending to the hilt. Already on Sunday evening, some Democrats were questioning how Barr could have so quickly decided that Mueller's findings did not support a charge of obstruction of justice against Trump.

The Democratic leaders in Congress, Sen. Charles E. Schumer (N.Y.) and House Speaker Nancy Pelosi (Calif.), in a joint statement, shifted the spotlight from the bottom-line finding of no collusion to a call for more transparency and the release of the full Mueller report. "The American people have a right to know," they said.

Even if both sides stick to their narratives in the coming months — "stop the witch hunt" vs. "what did the president know and when did he know it?" — that does not mean Mueller's work was pointless.

Mueller, Head of investigations into Russian interference in the 2016 U.S. Presidential Elections — Photo: James Ledbetter

The investigation, which has dominated the news and the president's attention for nearly his entire time in office, was always about far more than the particulars of which Trump campaign officials had what contact with Russians.

Like Watergate, the Iran-contra affair and the Bill Clinton impeachment, the Mueller probe was an investigation but also a morality play, a vehicle for a national inspection of who Americans really are and what values and standards should define the country.

But prosecutors don't probe the nation's soul; they only search for facts and patterns. The searing process of deciding the nation's direction comes after the reports are filed, after the indictments and trials and congressional hearings have run their course.

In one scandal after another in recent American history, the initial investigation has led to congressional hearings and even impeachment proceedings, which in turn have either chipped away at a president's support (permanently for Richard Nixon, temporarily for Barack Obama) or solidified it (both Bill Clinton and Reagan bounced back quickly from investigations).

In recent years, the country's deepening partisan divide has dampened the impact of such investigations. When Republicans in Congress held hearings in 2016 on the deaths of four Americans in a 2012 attack on a U.S. compound in Benghazi, Libya, the final report neither found evidence of wrongdoing by then-Secretary of State Hillary Clinton nor had any measurable impact on public opinion about the incident.

Democrats called the two-year investigation a "witch hunt," Republicans said it showed that Clinton had misled the public and opinion polls showed that hardly anyone's mind was changed.

The investigations into Trump's acts both as a candidate and as president will now move into a more freewheeling phase, as multiple congressional committees and federal prosecutors' offices look into a vast constellation of alleged misdeeds, including Russian efforts to interfere with the U.S. election, Trump's finances, his inaugural committee's fundraising, his family foundation, his business operations after he assumed office and his alleged marital infidelities and payoffs related to them.

The country's deepening partisan divide has dampened the impact of such investigations.

Past presidential scandals tended to be either personal, such as Clinton's White House infidelities with Monica Lewinsky, or political, such as Nixon's campaign of dirty tricks and efforts to obstruct investigations. But the array of allegations against Trump spans from intimately private behavior to official actions in office, and there is as yet little sign of Trump's critics and investigators narrowing their focus.

"There's often a blurring of personal, old-fashioned corruption and more serious abuses of executive power in these investigations," Greenberg said. "In Watergate, investigators eventually chose not to make the bombing in Cambodia or Nixon cheating on his tax returns part of an impeachment," focusing instead on the core issue of crimes Nixon may have committed in his reelection campaign.

"With Trump," Greenberg said, "there are several things going on at once — the money, the sex and Russia. Democrats in Congress will have to decide what they want to look into and what impact that choice may have on public opinion."

On Sunday before the summary's release, both sides were already rehearsing the narrative of the coming period, with Democrats going on TV to say it is too soon to talk about impeachment and Republicans countering that the Democrats intend to impeach Trump no matter what.

"What Congress has to do is look at a broader picture," House Judiciary Committee Chairman Jerrold Nadler (D-N.Y.) said on CNN's "State of the Union." "We have the responsibility of protecting the rule of law . . . so that our democratic institutions are not greatly damaged by this president."

Sen. Ted Cruz (R-Tex.) countered that what Democrats are "basically saying is they're going to impeach the president for being Donald Trump."

The prospect of at least another 20 months of investigations, allegations and dueling narratives dominating the nation's debate and paralyzing its politics might not seem quite as exhausting if it carried with it the prospect of one side or the other winning over a clear advantage in public opinion.

In past scandals, investigations and a reshaping of popular views of the president have gone hand in hand, historians said. Reagan's popularity sank as Congress investigated his role in a secret arms deal to support anti-communist rebels in Nicaragua, but then sharply rebounded as Reagan waived executive privilege during the investigation and the U.S. economy surged.

Trumpism remains a powerful force.

Similarly, Clinton's popularity bounced back after he was impeached, and some Republicans in Congress broke with their party to support the Democratic president "because the constituents they represented did not believe Clinton should be impeached," Greenberg said. "Now, we're just in a different cultural moment in terms of willingness to break with party."

The Clinton impeachment was the moment that "hardened the political lines and made bipartisanship almost impossible," said Shirley. "We're still living with that today. It would take so much to drive a wedge between Trump and his devoted followers."

Yet a reckoning and a political realignment and redefinition of both parties are underway, even as Trumpism remains a powerful force. Democrats are diving into a debate over just how far to the left they want to travel to be perceived as an attractive alternative, and Republicans are biding their time, waiting to see how durable Trump's takeover of their party turns out to be.

"Only after Trump leaves office will there be a more frank discussion within the Republican Party," Shirley said. "People will make decisions when it's right for them. If the economy turns down, so will the support for Trump. Politics is always about self-interest — of the candidate and of the voters."