WASHINGTON — One theme ran throughout Joe Biden’s inaugural address in January 2021: “unity.”

Biden spoke the word nearly a dozen times, signaling that his driving ambition would be to overcome partisan divisions so deep-rooted that his predecessor, Donald Trump, broke tradition and didn’t bother to show up at the Capitol for the swearing-in.

“We must end this uncivil war that pits red against blue, rural versus urban, conservative versus liberal,” Biden said.

Four years on, the war still rages. As Biden faces re-election, the nation is locked in the same unrelenting tribal standoff that has been worsening in America for generations.

He isn’t giving up, allies said, and if he wins a second term he may look to appoint Republicans to Cabinet positions and redouble efforts to make American political discourse less toxic. But that’s not so easily done.

A Vanderbilt University study that measures national unity shows a steady decline since the early 1980s, with a small uptick after Biden took office only because the number of people who “strongly disapprove” of the president softened a bit after Trump’s departure, said John Greer, the Vanderbilt political science professor who created the index.

In a focus group last week, a 46-year-old Georgia Republican said a reason she switched from Trump to Biden in 2020 was the hope that Biden’s victory might give way to more national cohesion. Disillusioned with what she has seen, she now plans to switch back to Trump.

“I went based on thinking that the world wouldn’t be as divided,” she said in the focus group, conducted by Engagious/Sago as part of its Swing Voter Project. “Things would get better; people would make nice. And we’re kind of back in that same boat again. Only worse, to be honest.”

For years, Democratic officials have been predicting that the far-right movement gripping Republican politics will burn itself out — that the “fever” will subside when a string of electoral losses forces a reckoning inside the GOP.

“I think the fever will break,” Biden, then the vice president, told a reporter aboard Air Force Two in 2012, after Barack Obama was re-elected.

“You will see an epiphany occur among many of my Republican friends,” Biden said in 2019 during a presidential campaign appearance in New Hampshire.

It never happened. There has been no epiphany, no civic awakening. Trump was voted out of office in 2020, yet the man and his MAGA movement are on the cusp of reclaiming power. Trump is running about even with Biden in national polls.

His acolytes hold leadership positions in Congress and are among its most prominent members. One, Rep. Marjorie Taylor Greene of Georgia, called for a “national divorce” last year, with the nation splitting into red and blue states.

Far from bringing about a national rapprochement, a Trump defeat could set off a round of political violence rivaling that of Jan. 6 as his embittered supporters mount protests over a result that neither he nor they accept as valid, current and past officials caution.

Trump himself wouldn’t rule out the possibility of violence by his supporters if he loses in November.

“I think we’re going to win,” he said last month. “And if we don’t win, you know, it depends. It always depends on the fairness of an election.”

Tom Daschle, a former Senate Democratic leader from South Dakota, likened the national mood to a “political cancer that is metastasizing.”

“I’m concerned about what happens if Trump does lose and whether or not we have a repeat of Jan. 6,” he said.

One difference, of course, is that Trump won’t be in the White House in the weeks following this election. Regardless of the outcome, Biden will still be empowered — and required — to “preserve, protect and defend the Constitution” until Jan. 20.

Biden hasn’t given up on the notion that the parties can reach some sort of détente. Nor has he abandoned the idea that victory in November might spur Republicans to renounce Trumpism, people familiar with the matter said.

They point to significant legislative wins during Biden’s term as proof that cross-party deals are possible even in the current climate when important national interests are at stake. Most recently, he signed a law sending billions of dollars in aid to Ukraine so it can fend off a Russian invasion that threatens the post-World War II order.

If Biden wins in November, he’d be better positioned to ease the polarization, his allies contend. He could carve out a distinct historical role if he could bring about a thaw in partisan animosities, without having to worry about a backlash from his liberal base. Biden, a product of a more collaborative era in Washington, wants to reach consensus, making him a good fit for this fraught moment, some who have worked with him said.

“President Biden is uniquely qualified to find ways to work together to get things done,” a senior White House official said. “Everything about his presidential leadership fits with that kind of effort.”

Allies expect Biden in a new term to appoint Republicans to more high-profile positions in his administration, which Obama tried. He kept Robert Gates, an appointee of Republican President George W. Bush, as his defense secretary and later appointed Republican former Sen. Chuck Hagel to the same post. Ray LaHood, a well-respected Republican representative from Illinois, was Obama’s first transportation secretary. But Biden saved the plum Cabinet jobs for loyal Democrats.

“I think if Joe Biden gets re-elected, there is a good possibility that there could be a Republican in his Cabinet,” Ted Kaufman, a longtime Biden confidant and Democratic former senator from Delaware, said in an interview.

The White House didn’t reply to a request for a comment on the record.

Blaming Biden for the persistent hostility between the parties may be too simplistic, officials argued. He entered office two weeks after the riot at the Capitol, which disrupted the peaceful transfer of power. To this day, Trump insists that the 2020 election was stolen, implying that Biden doesn’t legitimately hold office.

It’s hard to find a willing partner if the other side believes without evidence that you’re a fraud — or addled. Former House Speaker Kevin McCarthy, R-Calif., mocked Biden’s age last year during a tough set of budget negotiations, offering to take “soft food” to the White House for lunch.

“When you have Donald Trump continuing to run for president and continuing to divide the country, it’s very hard for the president, despite all his efforts, to achieve that goal” of national unity, said Sen. Chris Van Hollen, D-Md. “It’s not that defeating Donald Trump will result in harmony breaking out around the country. I don’t want to overstate it, but I do think that by defeating Donald Trump in this election, we’ll take some of the poison out of the national discussion.”

Still, Biden may have passed up some ripe opportunities to defuse tensions and project a more bipartisan image, others said. Former Rep. Adam Kinzinger of Illinois is a Republican who repudiated Trump, serving on the congressional panel that investigated the attack on the Capitol on Jan. 6, 2021. He is the sort of independent-minded Republican whose exile in the Trump era has made bipartisan collaboration in Washington more difficult.

Kinzinger credits Biden with “doing more than I expected and more than people give him credit for” in promoting bipartisanship. He said that in January, a Biden campaign staffer called him and suggested they would use him in the campaign once Trump’s rival Nikki Haley dropped out of the race. But Haley ended her campaign more than two months ago, and, he said, he has still not heard anything from Biden world.

“There are 20% of Republican voters who are still voting for Nikki Haley” in the GOP primary race, Kinzinger said. “Those are gettable people!

“I don’t say it because I need the ego boost. I say it because what the hell are they [the Biden campaign] doing?”

For differing reasons, Republicans of various political stripes believe Biden should have slammed on the brakes and prevented efforts to hold Trump accountable for alleged crimes.

Sen. Mitt Romney, R-Utah, told MSNBC host Stephanie Ruhle last week that Biden could have helped himself — and hurt Trump politically — by issuing a pardon from federal charges and leaning on New York prosecutors to drop their hush-money case against Trump.

“You may disagree with this, but had I been President Biden, when the Justice Department brought on indictments, I would have immediately pardoned him,” Romney said. “Why? Well, because it makes me, President Biden, the big guy and the person I pardoned a little guy.”

McCarthy said Biden had a reservoir of goodwill on Capitol Hill from his time as vice president, when he often played the role of deal-maker for Obama. That began to dry up even before Biden took the oath of office, McCarthy said in an interview.

“I think he started out and missed an opportunity. I think when he got elected, he watched the Democrats go and impeach Trump again,” said McCarthy, who at one point was sharply critical of Trump’s behavior on Jan. 6. “He should have stepped in at the time that the country saw this and said, ‘No, we’re not going to do that.’”

On policy, McCarthy, whom right-wing forces within the GOP caucus ousted as speaker last year, said Biden has bowed to pressure from a left-wing faction inside the Democratic Party that gives him little space to cut deals with Republicans.

Noting Biden’s aggressive efforts to erase federal student loan debt, McCarthy said: “Would he be doing the student loans forgiveness again and again and again if he didn’t have such a hard time with young people right in his party?”

When a country is cleaved so deeply, there may be only so much a president can do alone. A Pew Research Center study found that at the midpoint of Biden’s term in 2022, the percentages of Republicans and Democrats who view each other as “immoral” had spiked since 2016.

Yet there are some constructive steps Biden and the nation might consider, officials and political scientists said. Daschle suggested that, if he’s re-elected, Biden should invite congressional leaders from both parties to Camp David, Maryland, during the December holidays to see whether they can forge a joint agenda — and then unveil it during the State of the Union address in the new year.

Others said there need to be deeper, structural changes in the way the nation governs itself. Pippa Norris, a comparative political scientist at Harvard University, proposes a system of expanded representation in Congress meant to ensure that smaller, fringe parties at least have a voice.

Germany and New Zealand use that approach, which could ease the frustration of voters who feel angered and disenfranchised by America’s winner-take-all, two-party tradition, she said.

As president, Trump devoted little energy to reunifying the country. Biden, if he’s given another term, will at least try, his allies contend.

“I know what kind of person Biden is,” said Hagel, who served with Biden both in the Senate and in the Obama administration. “And in his own mind, that [defusing partisan tensions] could be his greatest contribution to this country as he leaves office.”

This article was originally published on NBCNews.com