CHICAGO -- When President Donald Trump warned this week on Twitter that he would move to fix Chicago’s “carnage” if the city doesn’t, he might not have realized that the feds already had arrived.

And thank God that they have, because the ineffective, bumbling and corrupt Democratic machine that has run the city into the ground for the past 86 years has clearly demonstrated it can’t police itself.

It has taken the federal government to convict not just the most murderous gangbangers but also numerous corrupt Chicago and Illinois politicians. It has taken the federal government to thump the city’s police for excessive use of force.

But Trump is about more than crime when it comes to the nation’s urban centers. There are his promises to revive America’s deteriorating inner cities, of which Chicago has a surfeit. And if Trump intends to more broadly redefine the federal-city relationship by stepping in where the locals have failed, then he might also want to look into Chicago’s calamitous finances that have crippled the police department, schools and other vital municipal services while flogging its taxpayers.

The City of Sloping Shoulders would be the perfect laboratory for Trump’s promised repair work. Its schools are broke, yet it gives teachers raises and allows the Chicago Teachers Union to cap the number of charter schools the district can have. Extravagant pensions for public employees are crushing taxpayers and cutting into vital services. Neighborhood infrastructure is wanting. Residents and businesses are hightailing it out of the city and state.

The left ridicules Trump’s use of the word “carnage,” but it doesn’t do Chicago justice. “Catastrophic” and “calamitous” also should be thrown into the mix.

Here’s just one recent example of how the feds have needed to intervene in the Windy City: U.S. Attorney Zachary Fardon this month successfully prosecuted six leaders of the vicious “Hobos” gang—the worst of the worst—for racketeering conspiracy during a five-year reign of terror on the city’s west and south sides. During a four-month-long trial, the feds detailed five murders whose brutality rattled a federal jury and a populace that had become hardened to the daily murders.

It’s also up to the feds to prosecute the city’s and Illinois’ compulsively corrupt politicians. The U.S. attorney recently returned a corruption indictment of yet another Chicago alderman, Willie Cochran, but that’s hardly anything new. A former cop who ran as a “reformer,” Cochran had replaced his predecessor, Arenda Troutman, herself convicted on corruption charges. If found guilty, Cochran would be the 30th alderman convicted since 1972. The latest was in 2010, when Isaac “Ike” Carothers pleaded guilty to corruption; his father, William, also an alderman, had been convicted 27 years earlier. All in the family. Add to that a couple of city clerks, four governors and assorted other city, county and state officials—all prosecuted by the feds.

Don’t look to the Illinois attorney general (who is Lisa Madigan, daughter of Michael Madigan, the Democrat who runs the abysmal state as House speaker) or the Cook County state’s attorney, whose jurisdiction includes Chicago. The standard explanation for this hands-off policy is that the feds have the resources and money to do the heavy lifting. Or that the locals and feds shouldn’t duplicate efforts. Sure.

The simplest answer most likely is the correct one: Local officials lack the courage or will to go after their own. It’s The Chicago Way, whose practitioners have turned the town into a crooked, violent and insolvent place.

So, will federal intervention fix it? (In a tweet Tuesday, Trump threatened to “send in the Feds.”) Not as long as apathetic, blind or self-seeking Chicago voters continue year after year to turn over the keys to the city to the incompetent, dishonest and corrupt Democratic machine. Even Trump, with all his bravado and self-confidence, can’t overturn elections. Even in a town where voter fraud is legendary.

It’s hard to think what Trump has in mind. Maybe it would be just to fortify the local U.S. attorney, FBI and ATF offices, help out with illegal gun control and pay for more cops, as Chicago Mayor Rahm Emanuel urged Tuesday. He asserted that federal resources have been scaled back in recent years -- an odd complaint when, for the past eight years, a Chicago Democrat has occupied the White House.

As usual, Trump is vague about his threatened intervention. Maybe he’s planning to send some tanks and armored vehicles into Chicago’s south and west sides. Or more seriously, federalize the National Guard to patrol Chicago streets, much as president Dwight Eisenhower and John Kennedy sent in federal troops to enforce court-ordered integration. Would the troops engage in “stop and frisk” strategy, which Chicago police had successfully used until the ACLU and other left-wing idealists stepped in?

It’s equally hard to imagine what Trump has in mind when he assures Americans that he will fix their inner cities. Costly Great Society programs such as Model Cities haven’t worked so well. Is Trump thinking of doubling down on standard Democratic favorites by sending in more money for housing, poverty and other “programs” that were so popular in the 1960s and 1970s? For sure, Chicago pols, contractors, pay rollers and other beneficiaries would welcome a resurrected War of Poverty because that would mean funneling millions dollars into their hands. Never mind worrying about where Trump would find the money for such an effort.

Maybe he’s thinking of direct federal involvement in the city’s operations, sort of like a guardianship, thus subjecting Chicago to the whims and prejudices of a Washington bureaucracy. (Although Chicago wants to, it can’t realistically look to the state of Illinois for help because it is wallowing in its own financial swamp.)

Clearly, federal intervention is not necessarily a good thing. The controversial Justice Department report slamming Chicago police for use of excessive force ignored at least one important factor: It failed to criticize the city’s Democratic leadership for the department’s many alleged sins. That’s not the report’s only flaw, whose release just before President Obama left office was clearly done for political considerations.

Here we haven’t even discussed the legal niceties posed by the provisions of the Constitution’s 10th Amendment that protects the sovereignty of the states and their creatures, municipalities.

In addition, any increased federal involvement in Chicago’s chaos poses a theoretical challenge for conservatives who strongly believe in the principle of subsidiarity, state’s rights and the 10th Amendment.

But, what should be done when local and state governance fails the public interest and common good as spectacularly as they have in Chicago and Illinois? When the voters themselves choose to wallow around in the muck with the corrupt? For Trump and others, a strong federal hand might be the only answer, as it is when needed to “[e]nsure the domestic tranquility” of “we, the people.”

Meanwhile Chicago waits breathlessly, or fearfully, to learn what Trump plans to do for, or to, Chicago.