As Ulysses S. Grant prepared to take the presidential oath of office in March 1869, his predecessor, the impeached President Andrew Johnson, sneered that Grant was “a dissembler, a deliberate deceiver” and refused to “debase” himself by attending his inauguration, writes Grant biographer Ron Chernow.

Despite this bitter inauguration send-off, a generous Grant promised that he would govern “calmly, without prejudice, hate or sectional pride.” But, through his presidency, he faced a growing insurrection from Southerners defeated in the Civil War but determined to win the peace for their lost cause. And they largely succeeded, creating a racist Jim Crow South that survived for almost 100 years.

President-elect Joe Biden will take office Wednesday with a promise to repair this broken country and begin to heal its divisions after an ideological civil war waged by his twice-impeached predecessor, Donald Trump, who will be rudely absent. But Biden will make his inaugural address from inside an armed camp, ringed by what a senior security official says will be 26,000 National Guard and up to 15,000 police, FBI and federal law enforcement officers.

The FBI believes this overwhelming force will probably deter another mob like the one that stormed the U.S. Capitol on Jan. 6. Among the insurgents, “Leaders are telling followers: Don’t do D.C. We’ll live for another day,” says one official who’s involved in security planning and familiar with intelligence reports. But this problem is just beginning.

Biden’s fundamental challenge — even as he issues executive orders on immigration, climate change, the pandemic and a host of other domestic problems — is to root out the insurgency. A priority is to assess how deep it has spread within the military and law enforcement. Senior military officials tell me they have already identified 30 individuals among active-duty personnel, National Guard forces and veterans who might have been active in the Jan. 6 storming of the Capitol.

Gen. Mark A. Milley, the chairman of the Joint Chiefs of Staff, has started talking with the service chiefs about new programs to vet recruits, check their social media records, educate them better about their mission, and identify and eject any who have seditious ideas. The military has had experience with gang members — neo-Nazis, Crips and Bloods, MS-13 — and learned to expel them, fast.

A retired four-star who was a battalion commander a decade ago recalls an incident with a neo-Nazi in the 10th Mountain Division. Commanders initially thought they would move him to another unit, but they decided it was essential to discharge him, immediately. “We had to be very swift and strong in stomping it out,” he recalls.

Militaries prize loyalty and discipline, but they reflect the larger society they serve. When politics is fragmented, insurgent ideas can sometimes spread in the ranks like cancer. I’ve watched that happen with armies in Egypt, Lebanon, Syria, Iraq, Pakistan and a half-dozen African and Latin American countries.

Extremist groups are like cults. They often recruit members who are experiencing personal crises and become radicalized through what one commander describes as an emotional “gateway.” The military has gotten better at predicting military personnel who may be prone to suicide; they need similar tools for identifying potentially seditious behavior without threatening First Amendment rights.

To get a sense of how widespread insurrectionist feeling may be, I asked a longtime CIA paramilitary officer, with strong pro-Trump ties and close links with former Special Operations forces comrades who share his views. His assessment: The Capitol rioters were mostly “knuckleheads living in a fantasy world with their Facebook pages.” The military and FBI should be able to “weed out the kooks.”

That sounds reassuring. But this militant Trump supporter offered an ominous warning against overdoing the crackdown. “People will visit violence on those who visit it on them,” he said.

Top Biden officials have received stern advice from military commanders: Take a page from Attorney General Robert F. Kennedy’s war against the Ku Klux Klan in the South and the Mafia in big cities. These threats need to be “ripped out” with a dragnet that’s well targeted but uses every tool in the legal arsenal.

But even as the Biden administration attacks the most seditious members of the insurrection, it should consider a tactic that’s quite radical in the current political climate — listening to the other side. The Greek historian Thucydides observed that wars are caused not only by fear and self-interest but also by the intangible feeling we describe as “pride.” An attempt to ignore this sentiment among nearly half the population will end unhappily.

Biden begins a new day for the United States on Wednesday. His challenge will be to combine toughness with generosity — and yes, as the Bible says, to love those who might consider themselves his enemies by hearing out their grievances.

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