“If Chicago doesn’t fix the horrible ‘carnage’ going on, 228 shootings in 2017 with 42 killings (up 24% from 2016), I will send in the Feds!” tweeted Donald Trump, commander in chief of the United States Armed Forces, just before 9:30 p.m. Tuesday.

The tweet came after a broadcast of Fox News’ “The O’Reilly Factor,” which featured a segment that explored whether and how the federal government could intervene in Chicago to the stop the “carnage” in a city that  in the minds of some has come to represent weakened law enforcement, the lawlessness of black America, and the failures of Democratic leadership. “The question is, can President Trump override local Illinois and Chicago authorities and stop the murder?” asked O’Reilly.

The drumbeat of Trump’s war on Chicago has been growing louder in the past few months, but the new President has been using his Twitter account to advocate for federal intervention in Chicago for years.

Trump may have been tweeting in response to O’Reilly’s segment, but his threat to send “the Feds” into Chicago to fix the “carnage” has been building for some time now. His focus on the city isn’t rooted in actual concern for its citizens, however. Instead, Trump began speaking publicly about violence in Chicago to support an argument for the New York’ Police Department’s racist and unconstitutional Stop-and-Frisk practice. His continued characterization of the city as a violent hellscape has persisted, perhaps, to spite the city President Obama’s adopted hometown, but almost certainly to advance a distorted, racist view of black communities, which Trump conflates with “inner cities.” It’s a view that resonates deeply with the Americans who voted for Trump, but it could mean disaster for Chicago’s black residents—and black communities across the country—if it’s allowed to further infect public policy and discourse.

The drumbeat of Trump’s war on Chicago has been growing louder in the past few months, but the new President has been using his Twitter account to advocate for federal intervention in Chicago for years.

In 2013, following a ruling by a federal judge that the stop-and-frisk tactics used by the New York Police Department violated the constitutional rights of people of color, Trump tweeted, “Chicago is a shooting disaster-they should immediately go to STOP AND FRISK. They have no choice, hundreds of lives would be saved!”

With no regard for the reality of crime and law enforcement in Chicago, Trump’s focus on the city ramped up in direct relationship to the media’s coverage of it and, of course, his own political ambitions.

It’s worth noting that the Chicago Police Department is actually already engaged in a pattern and practice of unconstitutional stops and searches of its black and Latino citizens, and has been for some time now. In fact, according to a report by the ACLU of Illinois, Chicagoans were stopped by police more than four times as often as New Yorkers at the height of the NYPD’s Stop-and-Frisk practice. The ACLU also found that 72% of all those stops were of black Chicagoans—a group that constitutes just 32% of the city’s population. To be sure, these intrusive and illegal stops have had no measurable impact on the city’s murder rates or even on gun seizures.

With no regard for the reality of crime and law enforcement in Chicago, Trump’s focus on the city ramped up in direct relationship to the media’s coverage of it and, of course, his own political ambitions. In 2014, Trump tweeted that “Obama should work on a ceasefire in Chicago as well as Gaza,” but his references to the city really took off during the heat of his campaign for president.

“Crime is out of control, and rapidly getting worse. Look what is going on in Chicago and our inner cities. Not good!,” Trump tweeted in July 2016—a month that saw the Republican give several speeches at rallies, even while accepting his party’s nomination, that cited violent crime in Chicago. By August, Trump was claiming that Chicago’s violent crime would go away in a week if he were elected and the city’s cops were allowed to be “tougher.” That month, Trump also used his Twitter account to share news that basketball star Dwyane Wade's cousin had been shot and killed in Chicago, a tragedy he used somehow to project that he’d win the black vote.

We've heard this tune about black crime from politicians before—never with a tweet-by-tweet drumbeat, but we've heard it.

During a late-September visit with Don King to a church in Cleveland, Trump answered a question about reducing violence in black communities with calls for Stop and Frisk in Chicago. Days later, while answering a debate question from Lester Holt about “healing” America’s racial “divide,” Trump again pivoted awkwardly to the Windy City. “We have a situation where we have our inner cities, African-Americans, Hispanics, are living in hell because it's so dangerous. You walk down the street, you get shot,” he said. “In a place like Chicago, where thousands of people have been killed, thousands over the last number of years. In fact, almost 4,000 have been killed since Barack Obama became president, over—almost 4,000 people in Chicago have been killed. We have to bring back law and order.”

Finally, while Trump was waiting to be sworn into office at the top of this year, he set his social media sights on Chicago once more. “Chicago murder rate is record setting - 4,331 shooting victims with 762 murders in 2016. If Mayor can't do it he must ask for Federal help!” he tweeted.

Given that history, Trump’s comments on the “poverty in our inner cities and the crime and the gangs and the drugs that have stolen too many lives” during his inaugural address, and the presence of a "Standing Up For Our Law Enforcement Community” page on the renovated White House website, his tweet about sending “the Feds” into Chicago takes shape as more than a just stray thought. Indeed, it appears to be a serious threat from Trump to introduce federal law enforcement into a local dynamic he barely understands, without any regard for city or state rights.

Trump has yet to detail exactly what he means by “send in the Feds,” but during the “O’Reilly Factor” segment that triggered his tweets, host Bill O’Reilly suggested that the president send the National Guard into Chicago’s black neighborhoods. Doing so suggests the imposition of martial law in the United States, a measure that would essentially transform a major American city into a test zone for Trump’s authoritarian instincts and his approach to civil law and rights.

We've heard this tune about black crime from politicians before—never with a tweet-by-tweet drumbeat, but we've heard it. It has given us racist and authoritarian policies for hundreds of years and, in the 20th century, a War on Drugs that spurred mass incarceration. If Trump has his way, it'll lead to a War on Chicago and everything that city represents in the public imagination. That’s bad news for Chicago's black residents, but also for our democracy.