It’s astounding that there hasn’t been more outrage at Mayor de Blasio’s threat to use the power of New York City’s purse to try to shut up Donald Trump. Doubly so, given that he’s doing so in the middle of an election.

It was bad enough for a Chicago alderman to threaten to block a Chic-fil-A franchise restaurant in his district because its owner, Dan Cathy, opposes same-sex marriage. The mayor of Boston, Thos. Menino at the time, grumbled a similar threat. But this is New York, press capital of the world and the most magnificently diverse city in the nation.

How is it possible that a mayor of New York can start threatening to allocate spending taxpayers’ money based on the political opinions of a company’s owner? It’s not that I sympathize with Mr. Trump’s remarks, particularly since on a net basis new immigrants generally are less likely to commit crime than native-born Americans.

Like my former colleagues at the Wall Street Journal editorial page, I’m for free minds and free markets, favoring the unfettered movement of trade and capital and, therefore, also of people. So while I favor enforcing our immigration laws, I’d also support radically loosening them.

There will come a time — and the sooner the better — when we have the kind of economic growth that will leave us praying for more immigrants from Mexico.

Neither, incidentally, do I differ with the mayor about how the “values of inclusion and openness” are ones that “define us as New Yorkers.” The city’s mosaic is one of the reasons so many of us love living here and, often, find other cities less exhilarating. But what about the First Amendment? What about the precedent?

If the city’s going to review its contracts with Donald Trump’s companies because of his political views, what about the views of all the other companies with which the city has contracts? This story erupts amid a growing tendency on the left to try to silence those with whom it disagrees. It’s one of the most disturbing trends in the country today, as it was last year when Governor Cuomo treated New York to a tirade about extremists.

Remember that? That was when Mr. Cuomo included among “extreme conservatives” who have “no place in the state of New York” those who are “right to life” and “pro-assault weapon.” That’s “not who New Yorkers are,” the governor growled. It was absurd for Cuomo, or any politician, to talk like that, particularly to include on his list such apple-pie issues as the Second Amendment and the right to life.

Not even Mr. Cuomo, though, was prepared to start reviewing state contracts with companies whose owners held such views.

And oh how the liberals were up in arms when Mayor Rudy Giuliani wanted to cut city funding for the Brooklyn Museum after it put on display a painting of the Virgin Mary splattered with elephant dung and pornographic pictures. That case actually got to federal court, where a district judge, Nina Gershon, forbade the city to try to eject the Brooklyn Museum from its subsidized quarters. Not one liberal seemed to care how offensive the painting was to Catholics.

Yet where are all the liberals who cheered her on now that Trump is the target? Where was Melissa Mark-Viverito? The City Council speaker is now saying that “people should rethink about their business relationships.” She added, “I hope it’s sustained, that it doesn’t become something that is just a couple of weeks or months.”

Look, I’m about as pro-immigration as they come. I’m for open borders and economic growth. We’re an under-populated country in desperate need of more potential employees. But the issue that has surfaced in the case of Donald Trump is one of the basic liberality of New York.

And the illiberality of the Democratic Party and the American left. They have as much to answer for as he does. Maybe Ms. Mark-Viverito and Mr. de Blasio will have someone do a painting of Donald Trump splattered with elephant dung and pornographic pictures.

Then they can go to court and try to force the city to pay for it.

This column first appeared in the New York Post.