By Petula Dvorak / The Washington Post

The plywood has returned. The fencing is coming back. Capitol Hill in Washington, D.C., is hunkering down again.

We remember this.

Twenty years ago, on the day after the Sept. 11 attacks, we shifted our daily alert level to red. The law enforcement officers who waved to neighborhood kids and patted our dogs began carrying huge weapons across their chests. We bought duct tape and plastic sheeting to protect against a chemical weapon attack. Every bit of powdered-sugar doughnut residue or spilled Splenda packet was treated like a hazmat scene.

The enemy (unless you were a bigot who turned on our fellow Muslim or brown-skinned Americans) was on the outside; terrorists from another land attacking the United States. And most folks (unless you were Muslim, victimized by the bigots) fondly remembered a shared unity in those days.

How we’ve changed in 20 years.

Who are those fences keeping out now?

They’re for the folks who call themselves American patriots; the disgruntled, bitter, hateful splinters of a nation that has turned on itself and left it utterly, hopelessly divided.

“There is little cultural overlap between violent extremists abroad and violent extremists at home,” President George W. Bush said in an extraordinary speech at the Flight 93 National Memorial in Shanksville, Pa., on Saturday.

“But in their disdain for pluralism, in their disregard for human life, in their determination to defile national symbols, they are children of the same foul spirit,” he said, “and it is our continuing duty to confront them.”

Capitol Hill is preparing for another demonstration against the law and order and democratic process the protesters profess to love. This Saturday’s gathering is to decry the arrests of more than 600 people who breached the Capitol on Jan. 6.

“The fence will go up a day or two before,” said U.S. Capitol Police Chief Thomas Manger, after meeting with members of Congress on Monday to brief them on how he’s going to handle the “Justice for J6” clowns. “And if everything goes well, it’ll go down, come down very soon after.”

Justice for the hoodlums of Jan. 6? I’m all in.

So far, the several dozen who have pleaded guilty are getting justice lite, with home confinement sentences, probation, even a diet of organic meals.

The extremists are already here. Like the ones who came on Jan. 5 and scoped out the Capitol or planted pipe bombs in my neighborhood, on the streets where my kids walk to school and thousands of people walk to work; they’re already in the city.

On Monday around midnight, police questioned a California man who was in his truck — a black-and-red Dodge Dakota decorated with swastikas and other white supremacist symbols — outside the Democratic National Committee headquarters on Capitol Hill.

They arrested Donald Craighead, 44, of Oceanside, Calif., for the multiple knives, a bayonet and a machete that they said were in his truck after he told them he was “on patrol” and shared some of his white supremacist views with them. (Sorry, we’re anti-bayonet out here, Don.)

In other times, seems we’d celebrate the arrest of those who befouled our nation’s capital and attacked our law enforcement officers.

Now we have Americans willing to stand on the memories of the dead to score points.

The Fairfax County Republicans sent out an emotional, vivid description of the Sept. 11 attacks in the form of a fundraising letter last week, complete with photos of the burning buildings. And then they pivoted right back to today’s conservative talking points.

“Please help us fund the critical grassroots services that will turn Virginia RED again and start the nationwide rejection of Democrat Marxism and end of American decline,” said the letter, in which they pledge to elect conservative leaders to “reject the appeasement of menacing fanatics, who will reject the poisonous Marxist doctrines of Critical Race Theory and racial/ethnic division, and who will reject the scurrilous notion of America’s best days being behind us.”

Our best days are when we are a united nation, when Bush made it clear that the enemies are not among us.

A week after the 9/11 attacks, Bush visited a mosque; a symbolic visit of unity before the Iraq invasion.

“The terrorists are traitors to their own faith, trying, in effect, to hijack Islam itself. The enemy of America is not our many Muslim friends; it is not our many Arab friends,” Bush said in a speech a little more than a week after the attacks. “Our enemy is a radical network of terrorists, and every government that supports them.”

In the years following those days of unity, America began shredding itself.

And it must be our goal to repair and rebuild, to discipline the children of that foul spirit.

Petula Dvorak is a columnist for The Washington Post’s local team. Follow her on Twitter @petulad.