Michael Barone: As in the 1960s, violent rioting hurts the most disadvantaged.

“America is burning. But that’s how flowers grow.” So spoke Massachusetts Attorney General Maura Healey.

“Riots are an integral part of the country’s march toward progress.” So read a statement from the Democratic Committee of Fairfax County, Virginia, the affluent Washington suburb that has a population of 1 million.

“Please, show me where it says protesters are supposed to be polite and peaceful,” asked CNN’s Chris Cuomo. He’s apparently been too busy interviewing his brother, the governor of New York, to reread the First Amendment, which protects “the right of the people peaceably to assemble.”

I take a different view. I know how violent rioting, and that’s what we’ve been seeing, despite media attempts at hiding it, can destroy a city and ruin the lives of its residents. In the summer of 1967, I was an intern in the office of the mayor of Detroit when the city suffered a six-day riot in which 43 people died. I was at the mayor’s side in the so-called command center as radio calls came soon after nightfall. Police were abandoning 1 square mile after another.

The riot finally ended after some 12,000 federal and federalized national guard troops restored order. But most of Detroit has still never fully recovered. You can still see the abandoned commercial structures and the residential streets with burned-out houses and hauntingly empty lots.

Downtown and adjacent areas have enjoyed a revival, which I hope will continue. But the lesson is clear. Violent riots destroy people’s willingness to invest their lives and money in a city. Those most harmed are those who start off the most disadvantaged. Violence and crime are a confiscatory tax on what people would otherwise earn and accumulate over a lifetime.

The combined effects of the COVID-19 lockdowns and the last several days’ rioting threaten to destroy the efflorescence of gentrifying central cities, which has followed Rudy Giuliani’s demonstration in New York City, a quarter-century ago now, of how to reduce and nearly eliminate violent crime. The demonstration these last few days that it can be suddenly increased threatens to undo that progress for the next quarter-century.

The short-term political effects are harder to gauge. A Morning Consult poll showed a 58% to 30% majority, unusual in these polarized times, supporting “calling in the U.S. military to supplement city police forces.” Will President Trump and Republicans benefit from their calls for “law and order,” as President Richard Nixon and Republicans did in the years after the riots in Detroit and many other cities half a century ago? Maybe, and especially if folks like Healey and the Fairfax County message poster are seen as representing the Democratic Party.

But unlike Nixon in 1968, Trump in 2020 is the incumbent president. Incumbents’ first duty is to maintain order and keep things from spinning out of control. Trump might be in trouble if voters come to agree that, as Fox News’s Tucker Carlson put it in his Monday monologue, “No one in authority is keeping order.”

The late political scientist Nelson Polsby called 1968 — with its King and Kennedy assassinations, multi-city urban riots, and violence outside the Chicago Democratic convention — the most awful election year in American history. So far, 2020 is looking like a competitor for that title.

“The moment has come for our nation to deal with systemic racism,” Joe Biden tweeted. Doing so, he might argue, is the only way to get things under control. But one might ask why that moment didn’t come earlier — if not in the 36 years he served in the Senate, then in the eight years he served as an active and involved vice president in the administration of President Barack Obama.

The uncomfortable fact is that the election and reelection of the first African American president did not produce the improvement in racial relations most of the public surely hoped for.

Quite the contrary. In 2008, the Gallup Poll reported that 70% of non-Hispanic whites and 61% of blacks said “relations between blacks and whites” were very or somewhat good. Gallup showed similar results to that question in seven polls during George W. Bush’s presidency.

Feelings deteriorated under Obama. By 2015, only 45% of non-Hispanic whites and 51% of blacks said relations between the races were good.

One can debate how much of this deterioration was Obama’s fault, a subject for another day. But surely there was a widespread sense of disappointment that black-white relations had not become as harmonious as many expected or hoped. Violent rioting won’t help, do that, any more than they’ll grow flowers.