After decades of one-party rule in cities torn by violent crime, public education crises, chronic homelessness and growing taxpayer despair, Democratic mayors have finally found a friend.
President Donald Trump.
In Baltimore, San Francisco, Los Angeles and, just the other day, Chicago, Trump proves again just how helpful he can be to Democratic mayors.
He's their gift.
You doubt me? Then think back to biology class, where you learned about mutually symbiotic relationships.
The bee and the flower. The Egyptian plover and the crocodile. Algae and spider crabs. Or, if you're particularly fixated on algae, then try algae and fungus.
I'm not assigning the role of fungus to either Democratic mayors or the Republican president. But both sides benefit mutually.
Aiming at suburban and rural white working-class votes in swing states, Trump attacks historically broken big-city Democratic policy with a brazen, mocking vulgarity that outrages the mayors, living as they do within their blue bubble.
The mayors attack him right back, with vigor, playing to their voters by calling him a racist. Terrible insults are traded. It all gets so personal and tribal. And, as any political biologist would tell you, it's all quite predictable.
Trump becomes the orange-haired totem that Democratic mayors shake in rage above their constituents, just as he holds street gangs of illegal immigrants like MS-13 up to his faithful.
For the mayors, it's a no-lose scenario. In attacking Trump, they seek to cement disparate urban constituencies, such as African Americans and Latinos who otherwise compete for jobs and status in cities of limited resources like Chicago.
Stoking outrage over Trump's rhetoric allows them to try to keep these voters in line, even if such voters are the beneficiaries of historically low unemployment rates, particularly for blacks, in the current economy.
For Democratic politicians, particularly white progressives, there can be no diversity of opinion among black voters. Without African American voters in lockstep, there would be no national Democratic Party.
Democratic political professionals understand this clearly and are nervous about presidential candidates Elizabeth Warren and Pete Buttigieg. Neither tracks all that well with black voters.
What Trump's anger and pointed insolence gives big-city mayors is this: the gift of time.
Remember Trump, with characteristic vulgarity, denouncing Baltimore as a rat-infested city? Shrieks of rage followed, until someone remembered that, oh, yeah, Democrats once complained of rats in Baltimore too.
Chicago has rats. But it suffers from a deadlier plague: the never-ending street gang wars.
As Chicago has been run by Democrats for generations, and as Democrats seeking Latino votes embrace sanctuary city policies that thwart federal law enforcement, Trump targets the city he loves to hate.
Speaking to a friendly crowd at the International Association of Chiefs of Police convention, Trump targeted Chicago police Superintendent Eddie Johnson, who boycotted the McCormick Place appearance.
"There is one person who is not here today. We're in Chicago. I said, 'Where is he? I want to talk to him.' In fact, more than anyone else, he should be here, because maybe he could learn something," Trump told the crowd. "Here's a man who could not bother to show up for a meeting of police chiefs, the most respected people in the country, in his hometown and with the president of the United States. And you know why? It's because he's not doing his job."
The other chiefs applauded Trump after his takedown of Johnson and Chicago's sanctuary city policy.
When he arrived in Chicago, no officials went out to meet Trump. Only Kevin Graham, president of the police union.
I personally believe that Eddie Johnson is doing his job, or at least trying desperately to do so, even though the city's street gang wars will likely claim some 500 lives, with well over 2,000 shot, by the time 2019 ends.
But Trump's attack did give Johnson's boss, Mayor Lori Lightfoot, a chance at parallel ridicule, and to be on the same side as anti-Trump protesters from the Chicago Teachers Union, who've been on strike against Lightfoot's government for almost two weeks.
In a tweet she said:
"It's no surprise that (Trump) brought his insulting, ignorant buffoonery to Chicago. Luckily, in this city, we know the truth and we will not let anyone -- no matter how high the office -- denigrate who we are as a people or our status as a welcoming city."
The next day, with Trump gone off to deal with Impeachment Theater in Washington, things were back to normal.
The striking Chicago Teachers Union, led by militant, hard-left bosses, continued their strike, though they've been offered a generous 16-24 percent raise over five years. And some 300,000 students -- mostly minorities from low-income neighborhoods -- had no school. Again.
And Republicans like Trump can't be blamed for that.
An exasperated Lightfoot asked: "Are we really keeping our kids out of class unless I agree to support the CTU's full political agenda wholesale?"
In a word, yes.
When Trump is in a big blue city, media focuses on him rather than on the mayors and the problems that have taken generations of Democratic policy and generations of misery to shape.
Liberal commentators who'd rather not take a risk and weigh in on a Democratic family feud like a teachers strike bravely bash Trump with glee.
The Republican president asks for it. And Democratic mayors give it to him.
It's not the bees and the flowers, exactly. Instead it's all about distraction, emotion and herding votes.
But the feeling is (symbiotically) mutual.