For more than a year, President Biden lacked a central idea for his administration.

In 2020, Biden vowed to defeat two scourges — the coronavirus and then-President Trump. He fulfilled the latter of those promises just by winning the election. The former became gradually less important to the country as vaccines and repeated exposure changed COVID-19 from an existential threat to a manageable illness.

That left the Biden White House largely adrift, responding to legislative battles, Supreme Court decisions and foreign crises with a host of policies, some successful, others not, but no clear message for voters to grab on to — a pudding without a theme, to borrow Winston Churchill‘s phrase.

Now, thanks in large part to his old nemesis, Trump, Biden has a theme again:

“Donald Trump and the MAGA Republicans represent an extremism that threatens the very foundations of our republic,” he declared in his prime-time speech from Philadelphia on Thursday night.

“Tonight,” he said, “I’m asking our nation to come together to unite behind the single purpose of defending our democracy, regardless of your ideology.”

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Biden clearly believes in that message. It’s also true that Democrats see it as politically helpful: A majority of voters already view Republicans as too extreme on some issues, notably abortion. Biden’s speech sought to depict those extreme positions as part of a broader, threatening ideology — a drive toward authoritarianism.

Trump has helped greatly in that effort. The latest example came Thursday, just a few hours before Biden’s speech, as the former president said on a conservative radio program that he would pardon defendants from the Jan. 6 riot at the U.S. Capitol if he regained the presidency.

“I mean full pardons with an apology to many,” he said, denouncing federal prosecutors and judges. “It’s a disgrace what they’ve done to them. What they’ve done to these people is disgraceful.”

The emphasis on extremism motivates Democratic voters, already mobilized by the Supreme Court ruling that overturned Roe vs. Wade.

Democrats hope the issue can also widen the rift between the GOP’s Trump and non-Trump wings, giving Democrats an opening to peel some voters away from the opposing camp.

“Not every Republican embraces ... extreme ideology,” Biden said, calling on “mainstream Republicans” to join him in opposition to Trump.

Republican leaders, of course, recognize that threat. They’ve portrayed Biden as insulting voters.

Biden should deliver an apology for “slandering tens of millions of Americans as fascists,” House Republican leader Kevin McCarthy of Bakersfield said before the speech.

Pennsylvania, where Biden spoke, provides an excellent example of Democrats’ hopes to win by portraying Republican candidates as extremists: Multiple polls show the Democratic candidates for both governor and the Senate leading in the state, in large part because their Trump-backed opponents have alienated swing voters.

In positioning himself as a defender of democracy, Biden can legitimately claim to have made some progress on his campaign promise of greater national unity.

Over the last two years, Congress has passed significant bipartisan legislation, including a $1-trillion measure to upgrade the country’s infrastructure — including roads, bridges, water systems and broadband connections — and a bill to pump $280 billion into funding research and building up the domestic semiconductor industry. In both cases, the measures achieved goals that had been blocked by congressional stalemates for years.

And by at least some measures, the nation’s divisions have started to ease since Biden took office.

Political scientists at Vanderbilt University recently developed a Unity Index, aimed at tracking Americans’ “general sense of faith and trust in their political institutions.” The index, which tracks measures of political extremism, congressional polarization, protest and domestic unrest and other data on division, plots a steady decline in national unity from 1981, when the data-tracking started, through Trump’s presidency. Starting with Biden’s election, the index shows a slight rebound, including a drop in ideological extremism this year.

While “it’s way too early to say the country is out of the woods,” there is “some gain” in unity, said Vanderbilt political scientist John Geer.

At the same time, however, other measures have worsened. Pollsters at the Pew Research Center, for example, report a steady increase in the share of people in each political party who say that those in the other party are “more closed-minded, dishonest, immoral and unintelligent than other Americans.”

That sort of negative partisanship — choosing a party primarily because of fear or dislike of people on the other side — has become the hallmark of politics over the last two decades.

It comes as the U.S. struggles through a profound change from a majority-white country into a multiracial and multiethnic society. That demographic shift and the resistance to it from many white Americans have been the prime driver in widening the national division.

For now, the U.S. system has become “calcified,” with voters locked into party identities that they’re unwilling to depart from, as UCLA political scientist Lynn Vavreck and her colleagues John Sides and Chris Tausanovitch put it in a soon-to-be-published book on American politics, “The Bitter End: The 2020 Presidential Election and the Challenge to American Democracy.”

With the two parties almost evenly balanced at the national level, meaning that every election brings with it the chance of shifting power in Washington, that calcification “raises the stakes of elections — and makes them more explosive,” they write.

Meantime, at the state level, liberal and conservative regions are moving apart at an accelerating rate, widening the overall national division on issues such as abortion, LGBTQ rights, education and racial justice.

On both sides of the political divide, Americans sense that there’s trouble ahead.

A poll that CBS released Thursday found 72% of Americans called U.S. democracy “threatened.” Almost equal shares of Republicans and Democrats held that position. But each side sees the other as the cause.

Democrats cited the “potential for political violence” and “efforts to overturn elections” as major threats, while Republicans pointed to government having “too much power” and “people voting illegally.” Large majorities on both sides also objected to too much money in politics.

While each party blames the other, both sides are not equally culpable. Trump openly sought to overturn the result of a democratic election he lost, and his supporters have embraced his lies about 2020 as an orthodoxy from which they will not tolerate dissent, as shown by the overwhelming defeat of Republican Rep. Lynn Cheney in her Wyoming primary last month.

Moreover, Republican ranks include a significant number of people — not a majority, but a sizable chunk — who say they could potentially support political violence.

Polling last year by the Public Religion Research Institute found that nearly one-third of Republicans agreed with the statement that “because things have gotten so far off track, true American patriots may have to resort to violence in order to save our country.” Only about 1 in 10 Democrats took that position. The share of Republicans who agreed rose even higher among those who most trust conservative media or believe the falsehood that the 2020 election was stolen.

Trump didn’t invent the ideology that now goes by his name. But he gave it voice and broke the power of the GOP establishment that had tried to keep the party’s right wing in check, even as it sought the benefit of their votes.

He remains a singularly polarizing figure and, much to Biden’s benefit, one who refuses to relinquish the stage. The prospect of defeating him rallied Democrats in 2018 and again in 2020. Facing a midterm election with his public standing still dangerously low, Biden can’t be blamed for hoping for a three-peat.

The legal battle continued this week over the stash of classified documents Trump kept at his winter resort.

— On Wednesday, as Sarah Wire reported, the Justice Department used a court filing to reveal that it had evidence from multiple sources of an effort to obstruct the government’s investigation. After Trump’s legal team handed over some classified documents in June as required by a grand jury subpoena, the Justice Department “developed evidence that government records were likely concealed and removed from the storage room and that efforts were likely taken to obstruct the government’s investigation,” the filing stated.

— Trump’s lawyers responded with a brief the next day, Wire reported, in which they said the presence of sensitive government documents at Mar-a-Lago “should have never been cause for alarm.” The FBI‘s search and seizure of the documents was an unnecessary escalation of the “standard give-and-take between former Presidents and [the National Archives] regarding Presidential library contents,” they said. FBI investigators are probing potential crimes, including violations of the Espionage Act and obstruction of justice, related to highly classified national security documents found at Trump’s Palm Beach residence.

An eight-page inventory of the thousands of government documents removed in the FBI search was released Friday. It listed highly classified materials as having been stored in the same boxes as hundreds of unclassified documents, including newspaper and magazine clippings, and other items, such as clothing, Wire reported.

— When Republicans sought a candidate to take on Arizona Sen. Mark Kelly, a prime target this election season, the obvious choice was Doug Ducey, the state’s accomplished and relatively popular two-term governor, Mark Barabak writes. But when Ducey signed papers certifying Biden’s narrow 2020 win in Arizona, he signed his political death warrant with the party’s Trump-worshiping base. The result was a nominee, Blake Masters, whose provocative statements and problematic stances — on abortion, Social Security, Trump’s election lies — greatly enhance Kelly’s prospects and undercut Republican hopes of flipping a seat vital to control of the 50-50 Senate.

— If Nancy Pelosi leaves Congress at the end of the year, as is widely expected, her departure will deprive California of one of the most effective national political allies it’s ever had, Jennifer Haberkorn reported. In her years as Speaker of the House, Pelosi has quietly and relentlessly promoted progressive California-backed policies on topics such as climate change, drought and healthcare.

— Although Biden’s speech Thursday night was largely a sermon about the poisonous effect of political polarization, it was also 24 minutes of heavy political bombardment, Eli Stokols wrote. The speech sought to frame the November midterms as a choice between two diametrically opposed political philosophies, not a referendum on Biden’s first two years in office.

— USC pulled out of hosting a proposed Los Angeles mayoral debate because of concerns over the cost of security and the “escalating tension in modern politics especially as the November election approaches,” Benjamin Oreskes wrote. According to an Aug. 11 email from the university’s Dornsife Center for the Political Future to the groups sponsoring the debate, the decision came after the university conducted a threat assessment related to the event. The email noted that the Dornsife Center did not make the decision to cancel but was “bound by it.”

— The pledge by billionaire mayoral candidate Rick Caruso to put his holdings, which include the Grove shopping center, into a blind trust if elected drew fire from his rival, Rep. Karen Bass, and two government ethics experts who called it an inadequate step that would invite conflicts of interest, Julia Wick reported.

— The Legislature’s end-of-session rush produced a host of major proposals. Among the highlights:

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David Lauter is a senior editor at the Los Angeles Times, based in Washington, D.C. He began writing news in Washington in 1981 and since then has covered Congress, the Supreme Court, the White House under Presidents George H.W. Bush and Bill Clinton and four U.S. presidential campaigns. He served as Washington bureau chief from 2011 through 2020. Lauter lived in Los Angeles from 1995 to 2011, where he was The Times’ deputy Foreign editor, deputy Metro editor and then assistant managing editor responsible for California coverage.